It's VS Its

It's: (contraption) contraption of "it is"

It's nice to see you today!

What color is the glue stick? It's blue.

Its: (possessive adjective) possession of something with our proper name or specified gender. 

The dog wagged its tail when it was happy.

Never judge a book by its cover.

How to remember:

Put the contraption's source in your sentence. If your sentence would make sense with "it is," then you are correct! For example: "The bird flapped it's wings" is most certainly INCORRECT! Does this make sense?: "The bird flapped it is wings." For the record, correctly this sentence would state: "The bird flapped its wings."

~Little Miss Grammar~