How do you snog? someone please tell me?

I'm only 13. and i've never snogged A boy. i've been out with boys but never snogged them. but i've got a boyfriend now and i really like him, he said to me we can snog when i'm ready, I am but, i don't know how to do it.. it may sound stupid but i've never done it before, can someone give me some advice? thankks x