Add a new user using the form at the bottom of the page. Usernames can contain only alphanumeric characters and the underscore.
To edit a user email address client the user_id hyperlink. The email address will become a text field you can modify. When you move away from it by tabbing or clicking it will update. Multiple asynchronous updates are supported. There's no need to wait for one update to finish saving before making a change to another user.