Farie, just scroll to the top of this page as Serena says, You will see the words Log in click on it, then a window will pop up that will ask you to fill in your username & password and there will be a little box there for you to tick that will keep you logged in each time you come to this site. I think it says Log me on automatically each visit.
How do I know this? well when I first started, I kept on wondering why it was telling me that my username was already taken, so I made up another one with underscores on each side of my name.
Then I worked out that there was a Log in thingy at the top of the page.