When you register, you must fill in all the fields provided. Your username can be anything you want, but should not contain spaces, or special characters($, #, % etc).
You must make sure the email you enter is a valid address, as the activation link required to use your account will be sent here. If you do not have an email address, you can sign up for a free email account at a variety of places. Google's Gmail is a good place to start.

Once you have completed your registration, you should receive an activation email within a few minutes. Depending on your email provider/software this could be mistaken as spam, so make sure you check your junk email if it does not arrive within a few minutes.
Once you have the email, you should follow the link contained inside. This will activate your account, and complete your registration. You will now be able to login with the username and password you chose at sign up.