When should Its not have an apostrophe?

Its. It's is a contraction and should be used where a sentence would normally read "it is." the apostrophe indicates that part of a word has been removed. Its with no apostrophe, on the other hand, is the possessive word, like "his" and "her," for nouns without gender.

Should I have an apostrophe?

Any time you have "it's" or "its" in your writing, double-check the sentence. If you can say "it is" in its place, then you do need the apostrophe. Don't use an apostrophe unless you mean "it is."