A pronoun can replace a noun or another pronoun. You use pronouns like "he," "which," "none," and "you" to make your sentences less cumbersome and less repetitive.
Grammarians classify pronouns into several types, including the personal pronoun, the demonstrative pronoun, the interrogative pronoun, the indefinite pronoun, the relative pronoun, the reflexive pronoun, and the intensive pronoun.

Personal Pronouns

A personal pronoun refers to a specific person or thing and changes its form to indicate person, number, gender, and case.

Subjective Personal Pronouns

A subjective personal pronoun indicates that the pronoun is acting as the subject of the sentence. The subjective personal pronouns are "I," "you," "she," "he," "it," "we," "you," "they."
In the following sentences, each of the highlighted words is a subjective personal pronoun and acts as the subject of the sentence:

I was glad to find the bus pass in the bottom of the green knapsack.

You are surely the strangest child I have ever met.

He stole the selkie's skin and forced her to live with him.

When she was a young woman, she earned her living as a coal miner.

After many years, they returned to their homeland.

We will meet at the library at 3:30 p.m.

It is on the counter.

Are you the delegates from Malagawatch?

Objective Personal Pronouns

An objective personal pronoun indicates that the pronoun is acting as an object of a verb, compound verb, preposition, or infinitive phrase. The objective personal pronouns are: "me," "you," "her," "him," "it," "us," "you," and "them."
In the following sentences, each of the highlighted words is an objective personal pronoun:

Seamus stole the selkie's skin and forced her to live with him.

The objective personal pronoun "her" is the direct object of the verb "forced" and the objective personal pronoun "him" is the object of the preposition "with."

After reading the pamphlet, Judy threw it into the garbage can.

The pronoun "it" is the direct object of the verb "threw."

The agitated assistant stood up and faced the angry delegates and said, "Our leader will address you in five minutes."

In this sentence, the pronoun "you" is the direct object of the verb "address."

Deborah and Roberta will meet us at the newest café in the market.

Here the objective personal pronoun "us" is the direct object of the compound verb "will meet."

Give the list to me.

Here the objective personal pronoun "me" is the object of the preposition "to."

I'm not sure that my contact will talk to you.

Similarly in this example, the objective personal pronoun "you" is the object of the preposition "to."

Christopher was surprised to see her at the drag races.

Here the objective personal pronoun "her" is the object of the infinitive phrase "to see."

Possessive Personal Pronouns

A possessive pronoun indicates that the pronoun is acting as a marker of possession and defines who owns a particular object or person. The possessive personal pronouns are "mine," "yours," "hers," "his," "its," "ours," and "theirs." Note that possessive personal pronouns are very similar to possessive adjectives like "my," "her," and "their."
In each of the following sentences, the highlighted word is a possessive personal pronoun:

The smallest gift is mine.

Here the possessive pronoun "mine" functions as a subject complement.

This is yours.

Here too the possessive pronoun "yours" functions as a subject complement.

His is on the kitchen counter.

In this example, the possessive pronoun "his" acts as the subject of the sentence.

Theirs will be delivered tomorrow.

In this sentence, the possessive pronoun "theirs" is the subject of the sentence.

Ours is the green one on the corner.

Here too the possessive pronoun "ours" function as the subject of the sentence.

Demonstrative Pronouns

A demonstrative pronoun points to and identifies a noun or a pronoun. "This" and "these" refer to things that are nearby either in space or in time, while "that" and "those" refer to things that are farther away in space or time.
The demonstrative pronouns are "this," "that," "these," and "those." "This" and "that" are used to refer to singular nouns or noun phrasesand "these" and "those" are used to refer to plural nouns and noun phrases. Note that the demonstrative pronouns are identical todemonstrative adjectives, though, obviously, you use them differently. It is also important to note that "that" can also be used as a relative pronoun.
In the following sentences, each of the highlighted words is a demonstrative pronoun:

This must not continue.

Here "this" is used as the subject of the compound verb "must not continue."

This is puny; that is the tree I want.

In this example "this" is used as subject and refers to something close to the speaker. The demonstrative pronoun "that" is also a subject but refers to something farther away from the speaker.

Three customers wanted these.

Here "these" is the direct object of the verb "wanted."

Interrogative Pronouns

An interrogative pronoun is used to ask questions. The interrogative pronouns are "who," "whom," "which," "what" and the compounds formed with the suffix "ever" ("whoever," "whomever," "whichever," and "whatever"). Note that either "which" or "what" can also be used as an interrogative adjective, and that "who," "whom," or "which" can also be used as a relative pronoun.
You will find "who," "whom," and occasionally "which" used to refer to people, and "which" and "what" used to refer to things and to animals.
"Who" acts as the subject of a verb, while "whom" acts as the object of a verb, preposition, or a verbal.
The highlighted word in each of the following sentences is an interrogative pronoun:

Which wants to see the dentist first?

"Which" is the subject of the sentence.

Who wrote the novel Rockbound?

Similarly "who" is the subject of the sentence.

Whom do you think we should invite?

In this sentence, "whom" is the object of the verb "invite."

To whom do you wish to speak?

Here the interrogative pronoun "whom " is the object of the preposition "to."

Who will meet the delegates at the train station?

In this sentence, the interrogative pronoun "who" is the subject of the compound verb "will meet."

To whom did you give the paper?

In this example the interrogative pronoun "whom" is the object of the preposition "to."

What did she say?

Here the interrogative pronoun "what" is the direct object of the verb "say."

Relative Pronouns

You can use a relative pronoun is used to link one phrase or clauseto another phrase or clause. The relative pronouns are "who," "whom," "that," and "which." The compounds "whoever," "whomever," and "whichever" are also relative pronouns.
You can use the relative pronouns "who" and "whoever" to refer to the subject of a clause or sentence, and "whom" and "whomever" to refer to the objects of a verb, a verbal or a preposition.
In each of the following sentences, the highlighted word is a relative pronoun.

You may invite whomever you like to the party.

The relative pronoun "whomever" is the direct object of the compound verb "may invite."

The candidate who wins the greatest popular vote is not always elected.

In this sentence, the relative pronoun is the subject of the verb "wins" and introduces the subordinate clause "who wins the greatest popular vote." This subordinate clause acts as an adjective modifying "candidate."

In a time of crisis, the manager asks the workers whom she believes to be the most efficient to arrive an hour earlier than usual.

In this sentence "whom" is the direct object of the verb "believes" and introduces the subordinate clause "whom she believes to be the most efficient". This subordinate clause modifies the noun "workers."

Whoever broke the window will have to replace it.

Here "whoever" functions as the subject of the verb "broke."

The crate which was left in the corridor has now been moved into the storage closet.

In this example "which" acts as the subject of the compound verb "was left" and introduces the subordinate clause "which was left in the corridor." The subordinate clause acts as an adjective modifying the noun "crate."

I will read whichever manuscript arrives first.

Here "whichever" modifies the noun "manuscript" and introduces the subordinate clause "whichever manuscript arrives first." The subordinate clause functions as the direct object of the compound verb "will read."

Indefinite Pronouns

An indefinite pronoun is a pronoun referring to an identifiable but not specified person or thing. An indefinite pronoun conveys the idea of all, any, none, or some.
The most common indefinite pronouns are "all," "another," "any," "anybody," "anyone," "anything," "each," "everybody," "everyone," "everything," "few," "many," "nobody," "none," "one," "several," "some," "somebody," and "someone." Note that some indefinite pronouns can also be used as indefinite adjectives.
The highlighted words in the following sentences are indefinite pronouns:

Many were invited to the lunch but only twelve showed up.

Here "many" acts as the subject of the compound verb "were invited."

The office had been searched and everything was thrown onto the floor.

In this example, "everything" acts as a subject of the compound verb "was thrown."

We donated everything we found in the attic to the woman's shelter garage sale.

In this sentence, "everything" is the direct object of theverb "donated."

Although they looked everywhere for extra copies of the magazine, they found none.

Here too the indefinite pronoun functions as a direct object: "none" is the direct object of "found."

Make sure you give everyone a copy of the amended bylaws.

In this example, "everyone" is the indirect object of the verb "give" -- the direct object is the noun phrase "a copy of the amended bylaws."

Give a registration package to each.

Here "each" is the object of the preposition "to."

Reflexive Pronouns

You can use a reflexive pronoun to refer back to the subject of the clause or sentence.
The reflexive pronouns are "myself," "yourself," "herself," "himself," "itself," "ourselves," "yourselves," and "themselves." Note each of these can also act as an intensive pronoun.
Each of the highlighted words in the following sentences is a reflexive pronoun:

Diabetics give themselves insulin shots several times a day.

The Dean often does the photocopying herself so that the secretaries can do more important work.

After the party, I asked myself why I had faxed invitations to everyone in my office building.

Richard usually remembered to send a copy of his e-mail tohimself.

Although the landlord promised to paint the apartment, we ended up doing it ourselves.

Intensive Pronouns

An intensive pronoun is a pronoun used to emphasise its antecedent. Intensive pronouns are identical in form to reflexive pronouns.
The highlighted words in the following sentences are intensive pronouns:

I myself believe that aliens should abduct my sister.

The Prime Minister himself said that he would lower taxes.

They themselves promised to come to the party even though they had a final exam at the same time.

Personal pronouns, Possessive determiners, Possessive pronouns

Personal pronouns		Possessive determiners	Possessive pronouns
as subject (nominative)	as object (accusative and dative)
I	me	my	mine
you	you	your	yours
he	him	his	his
she	her	her	hers
it	it	its	its
we	us	our	ours
you	you	your	yours
they	them	their	theirs
1	2	3	4
We have some books.	The books are for us.	These are our books.	The books are ours.