To get started, you'll need to create the first user account. This account is a "superuser" account: it will be able to edit anything on the site. Therefore, you should use a strong password.
You can only create this account once, but if you like, you can change the username and password after it's created, or add new superusers afterwards.
The email address is used for password resets. You don't have to provide one, but if you don't, you won't be able to reset your password if you forget it.