The It's vs. Its

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 there is absolutely, positively, no such word as its'.

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.

Another test

Its is the neuter version of his and her. Try plugging her into your sentence where you think its belongs. If the sentence still works grammatically (if not logically) then your word is indeed its.

Examples

It's been good to know you. Contraction: it hasIt's a bird! It's a plane! Contraction: it is
The dodo bird is known for its inability to fly. Possessive pronoun: its inability = the dodo bird's inability.


this is the post for those who want to learn basic english language.
if any response is available then surely i'll keep updating this english section under languages label.