A pronoun is a word used instead of a noun. There are very many kinds of pronouns.

Personal pronouns

Read the following sentences:

I have seen him.
They have come.
We have invited them.
He has always helped me.
We bought it.
They are our friends.
She is a nice girl.

Here the words in italics are examples of personal pronouns. In grammar, the word person refers to the three possible subjects of speech: first person, second person and third person.
The first person stands for the speaker; the second person stands for the person spoken to; the third person stands for anyone or anything else.

First person

Read the following sentences:

I have a dog.
We bought a car.
Our dog is smarter than yours.
They have invited us.
A friend of mine lives abroad.
He called me.

The pronouns I, my, mine, me, we, us, our and ours are said to be in first person because they stand for the person speaking.

Second person

You are a good girl.
Which is your boy?
My cat is smarter than yours.

The pronouns you, your and yours are said to be in second person because they stand for the person spoken to.

Third person

He has a car.
She is a nurse.
They have arrived.
It is her bag.
She has invited her friends.
They don’t know its price.

The pronouns he, his, him, she, her, hers, they, their, theirs, them, it and its are said to be in the third person because they stand for some person or thing other than those included in the first and second persons.

Notes
Personal pronouns in the possessive case has two forms – my, mine; our, ours; your, yours; her, hers; their, theirs. Note that the forms my, our, your, her and their are used before a noun. They are actually possessive adjectives, and not possessive pronouns. The forms mine, ours, yours, hers and theirs are generally used after a noun.

This is my house.
This house is mine.
That is your coat.
That coat is yours.
It is their fault.
The fault is theirs.
He lost his pen so I lent him mine.

Possessive adjectives (my, your, his, her, their) cannot stand alone: they are always followed by a noun. Possessive pronouns (mine, yours, his, hers, theirs, ours) can stand on their own.

My car has come. Theirs hasn’t come yet. (= Their car hasn’t come yet.)
His home is small. Mine is big. (= My home is big.)
Your hair is black. Mine has turned grey. (=My hair has turned grey.)