It is an indescript, general pronoun for any singlular, something, animate or figurative.
If this something is doing something worth talking about, you can combine it and is to make the contraction it's (i.e. "Hey, Honey, it's about time to tune into the Weather Channel for the Local on the Eights.")
If this something possesses something else, perhaps a dog and his bown or a fish and her bowl, then you show possession by using its (i.e., its bone, its bowl). I know it seems like there should be an apostrophe, since it's showing possession, but that's just not how it works. Sorry, black and white legalists. Rules are made for exceptions.
You should never, ever, and also never, use Its'. For any reason. The apostrophe-s combo is reserved for plural possessives, and the very nature of 'it' is singular. You cannot have more than one it. Otherwise the word you want is theirs, a word that is inherently possessive and needs no apostrophe. Just when you think you've got it all straight. Bottom line: Never its'.
And so there you have it, in case you've been wondering, and I only write little ditty this because many of you tell me you have.
Feel free to discuss over dinner.