Possessive adjectives in English refer to the possessor and not to the thing possessed.

Examples:

• Tom’s father is his father but Mary’s father is her father
• A boy loves his mother but a girl loves her father
• The tree drops its leaves in autumn. (Note that its is different from  it’s (with an apostrophe). It’s means it is).
• The girls are playing with their brother.

To add emphasis, own can be placed after my, your, his, etc.  

Examples:

• My own car  – Her own bike

Possessive pronouns are used to replace possessive adjectives + nouns 

Examples:

• This is my book  – The book is mine
• This is our house  – The house is ours. 
• This is their car  – The car is theirs.