Yes you have entered puberty. that's about the age i entered as well. Masturbating is when you take your hand, you grab your penis when it is hard, and you stroke up and down until you reach orgasm. If you have never done this before, try it, when you feel like something is going to come out, keep going! you will get an orgasm and it will be the best feeling you have ever had. Every boy remembers their first orgasm
I remember mine 4 years ago lol.