I've seen several people mention that they have trouble remembering whether to use "its" with an apostrophe, so here's the answer. It's very simple:

"it's" means "it is" or "it has". Always. No other meanings.

(To test, replace "it's" with "it is" or "it has" and re-read
the sentence. Still make sense?" OK.)

In every other instance, use "its".


Hope this helps.