How to say "my" and "your" in Polish. Why we need 3 forms?

Talking about things or persons belonging to us is a really nice thing, isn’t it? We can talk about that for hours. We keep on talking even if people who are listening to us get bored quickly.
 Let’s try to talk about that in Polish!
 At first look it seems to be a bit complicated because the word “my” has 3 basic forms in Polish. The same is with a word “your” (singular).  “My” can be translated as mój, moja or moje in Polish. “Your” can be translated as twój, twoja or twoje into Polish. A right choice of a right form among these 3 forms depends on the gender of a noun which follows the word "my" or "your".