It's versus Its

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

For example: It's up to you. It's been a long day.

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

For example: The company lost its assets

Here is a simple test:

If you can replace it's in your sentence with it is or it has, then your word is it's; otherwise, your word is its.

And there is absolutely, positively, no such word as its'!