Fields Required when Inserting new Users to database

[Zantox]

Hello,

I've created my own global registration system, that registers to other services I offer, such as Mantis Bug Tracker.
I'm curious as to what fields need to be inserted to have a new user show up and what tables.
I assumed it was the 'user' table, and inserted a 'username' 'email' and 'password' but it didn't seem to work.
I feel like it needs to be inserted into other places as well?

Please Advise.