[So Cal Rocket]

It's is a contraction for it is or it has.

Its is a possessive pronoun meaning, more or less, of it or belonging to it.

And just for the record there is absolutely, positively, no such word as its'

[Polonius]

Thank you for pointing that out ... I see so many people using "it's" rather than "its" as a possessive pronoun, and it continually irks me.