For the username, enter something you will easily remember. It can be a mixture of letters, numbers and other characters but cannot contain spaces. Do not make it over complicated (like a password), as it should be easy to remember. DO NOT use your email address as your username.

Note that your username cannot ever be changed once it is set (hence the reason for not using your email address).

When you login you can then enter your username OR email address at the prompt (plus your password), to login.