Its : The word its is a possessive adjective for things and animals, similar to his and her. Ex :
1.The boy broke his leg.
2.The girl broke her leg.
3. The dog broke its leg.

it's : The term it's is a contraction, short for "it is" or "it has". Ex :
1. It's late.
2. I wonder why it's so cold.
3. It's not raining