I will not have you, in one night, besmirching that name by behaving like a babbling, bumbling band of baboons! - Professor McGonagall (Harry Potter and the Goblet of Fire)
Use it's (with the apostrophe) only when you mean "it is" or "it has." For example: It's time to go. (It is time to go.)It's been a long time. (It has been a long time.) Use its (without the...