It's called French kissing when you use your tongue.
An important tip to start: always try to swallow before you kiss. Moist, not wet.
Start slowly, use your tongue to caress his underlip. Keep your tongue moving. In time, probe deeper and deeper into his mouth.
Explore, retract your tongue, explore some more. Try to tease his tongue in following yours when you retract.
Don't overdo it, variation and surprises are the key to the fun.
Suck and nibble the lips in between the tongue-probing.
Every now and then, detour away from the lips, elsewhere on the face.
Get your hands in on the action. Caress his face, hold his neck and pull him to you.
Don't dominate the kisses. You are kissing together.
Stop in time. Make him want to come back for more.