If you are here to manage a domain name (e.g. change DNS servers or contacts) and you have been given a "billing id" and billing password, you need to go in through the my-account area. From there, click on domain-registrations, and then on the relevent domain.

The my-account area is the "prefered" management path, but older and more specific options are given below.

If you have a "domain management username", take the com/net/org link below. If you're the admin contact for a .CA domain, then you won't have a userid/password, but the .CA link below will suffice. If you aren't sure which userid and password you have, you can check the "Passwords, why so many?" link at the support index.