First time using chibi paint EVER. I could have done way better though..

This was just a quick spur-of-the-moment art, i had written ''kiss me i'm irish'' at the side but i took it off. I don't mind critics, but keep in mind i've only ever used MP before..
Anyway, can someone explain what ''layers'' are and how you use them?? I've heard them mentioned but i don't have a clue what they are.

Edit: Just saying, this is a chibi style drawing, and is supposed to be unrealistic
