How do I suck dick

So I really want to suck my boyfriend’s dick but I don’t know how exactly. I have a bad ish gag reflex and I’m worried about that along with the thickness but i really want to- it seems hot and I’d love to do it to him since he eats me out I just don’t know how to do it how do I move my head? I know i probably won’t be able to fit all of it in my mouth and throat maybe just the tip or few inches. Any tips would greatly be appreciated! And tips to make the gag reflex not be as bad? EDIT: TO THE GUYS DMING ME, STOP BEING CREEPS