Just try and follow his lips with yours, if you like you can try using your tongue and sort of "suck the kiss" (Ohhh yeah red hot chilli's)
With your hands put them wherever you feel most comfortable, he's your boyfriend he won't mind you holding him around the waste, thighs, back of his neck, chin, or whatever. If you like eachother it really shouldn't matter if you make mistakes and being that young it's only natural.

You can breath through your nose, and when you close your lips to re-kiss you can take a breath or swallow any saliver you had in your mouth (if you get me).

Just keep practicing, and you can always bit his lip, that's nice sometimes ;].