1. If a word is used instead of a noun, it is called a Prnoun.

e.g.   a. The boy is very happy. He is playing football.

In this sentence the word "He" stands for the noun "boy", so "He" is a pronoun. 

b. Mary is a good girl. She works very hard. 

In this sentence the word "She" stands for the proper noun "Mary" so "She" is a pronoun.

Personal Pronouns

2. Kinds of Pronouns and their uses :

A Personal Pronouns is used to replace the name of a person or thing.

e.g. I , you , he , she , it , they , we.

As subjects

Singular　　　　　　　　　　　Plural

I am a Pupil.　　　　　　　　We are pupils.

You are a pupil.　　　　　　　You are pupils.

He is a pupil.　　　　　　　　They are pupils.

She is a pupil.　　　　　　　　They are pupils.

It is a dog.　　　　　　　　　　They are dogs.

As objects

Singular　　　　　　　　　　　　　　Plural

My mother helps me.　　　　　　　　My mother helps us.

My mother helps you.　　　　　　　　My mother helps you.

My mother helps him (her).　　　　　　My mother helps them.

My mother helps it.　　　　　　　　　My mother helps them.

(A) The Personal Pronouns 'I' and 'we' - First Person.

(B) The Personal Pronoun 'you' - Second Person.

(C) The Personal Pronouns 'he', 'she', 'it' and 'they' . -Third Person.