i am assuming that your site is being hosted on a windows server, correct?
this is a very large question you are asking that involves many different things. first off you will need to learn how to interact with the database using asp. (tutorials:
ASP101) once you get that all figured out you can attempt to put together a basic system for user registration, login and user management. however, at this point the system probably won't be very secure. so you will need to learn about password encryption (hashing) and how to integrate it into your system.
the list of possibilities goes on and on.