Hi!
Well, it's not a simple question, i must say!
I would start creating a database, and normalise it.
Maybe something with user, login, pass, credits, hosting_package, session_id and so on...
Until you have everything in it you need.
grant yourself the rights to the DB and its tables, otherwise you won't be able to write anything into it.
As for the login thing:
Read up on sessions, with them you can keep track of just about anything, and assign anything to for instance banners (the credits for example) or anything else.
Let's say a user registers, you could store his/her login/pass etc.. with sessions, you can track every user on your page, and see what they're doing.
User select's package, package type can be stored in the DB, along with starting credits or something.
A banner link could hold the user's session_id or login name or something like that. With that you can update the database and call for a new banner when clicked, and update the credits in the DB.
Checking up on the credits in the DB can tell you if the user has reached the amount of credits nescesarry, update the DB set user's status to 'complete' or whatever..
I know this sounds a bit global, and it is, but like i said, it's not a simple question!
Regards,
thefisherman