1. The words its and it's are two different words with different meanings.
Example: The dog has hurt its leg./ He says it's two o'clock.

2. The words your and you're are two different words with different meanings.
Example: Here is your coffee. / You're looking good.

3. The words there, their and they're are three different words with different meanings.
Example: Do you think they're happy? / I saw their new car.