acrobat  

I can never work out my apostrophes. Such as, do I write "it's" or "its"?

I used to get confused, but I've worked it out now

"it is" can be shortened to "it's" because the aposotrophe stands in for the missing letter...

...but if you write "its", that is a bit like saying "my" or "your", so you could write "the cat licked its whiskers"