Pronoun is a word used in place of nouns, people, animals, things, places.
It avoids repeating words that have already been mentioned.  Pronoun can act as both subject and object in sentences such as I, You, We, They, He, She, It.  

Pronouns can be divided into 1st, 2nd, and 3rd person pronouns.                   

Pronouns can be divided into the following 5 types:

 1. Relative Pronoun serves to expand the sentence to the subject or object to add details. It precedes            the Relative Clause and connects complete sentences.  Relative Pronouns include who, which, that, whom, whose, where, and when.

2. Possessive Pronoun is a pronoun that says this is yours, that is mine. 

Including mine, yours, his, hers, its, ours, theirs, etc.

3. Reflexive Pronoun (self/reflexive pronoun) which is a word that reflects the Subject Pronoun (I, You, We, They, He, She, It) is used when the subject and object are the same person or group of people.  Self-pronouns include the word "self" or "selves" at the end.

such as myself, herself, himself, yourself, yourselves, themselves, and ourselves.

4. Demonstrative Pronoun are this, that, those, these, one, ones to indicate which 

this, that, that, which one is what.

5. Interrogative Pronoun is a pronoun used to ask questions in interrogative sentences.

Including what, who, whom, whose, which, etc.