how do I add my ipad to the account

Go onto settings on your ipad

on the very top right press it should say sign in

sign in with your apple email and password, if you forgot watch this video https://www.youtube.com/watch?v=LIOapHreNe4 (apple support)

verify on your iPhone

any problems reply

Sign-in the iPad using the same AppleID.

If I’m misunderstanding your question, sorry.