First of, it’s a game. Relax.

Second, he’s a teen and his likes and attention will shift in seconds at times. But he will remember the time with you, in a good way, eventually.

Next, pick a version of D&D both of you want. Me, I’m old school and even though I’ve tried all but 4e (I even bought the 5e core books and a few add-on books), I still prefer 1E.

Then read through the Player’s Guide and DM’s Guide with a one-pass through nind. Now this part is important, take notes of what doesn’t make sense. Don’t stress over those things. Just take notes. Then ask here of someone.

Then with notes and replies in hand, read again for clarity.

Now, find a prebuilt module/adventure. Preferably for a single player. There’s a ton of them. Look online. Read through that, take notes, ask, read again.

THEN play.

Remember though, it’s a game. Mistakes will happen. Accept that, adjust, move forward.

You’re at the kindergarten stage. You and he can’t expect college level games, yet.

Lastly if you both decide on 5e, grab the original Starter Set. Do as I said above. Run it as is, it’s intended to be easier. Don’t allow beyond what’s in the reduced rules. It’s designed around them.

After finishing the include adventure, get the original. Essentials Kit. Do the same.

Then go buy the books. You’ll find original 5e and the new “One” socially modified books. Pick your poison. Do what I direst said.

You’ll do fine.