Existing users are listed in the lower left area of the sidebar. If there are many user accounts on your MySQL server, the field with the magnifying-glass icon may be handy for filtering the users you are looking for. Typing in t or T, for example, will set the filter to users whose names begin with a t. The filter works in a case-insensitive fashion.
If you are an experienced MySQL user, you will notice that users are not listed the typical MySQL way (user@host), but rather with their usernames only. If double-clicking on a username does not show subcategories for that user, this means that the user's privileges are not restricted to a specific host, or hosts. If there are subcategories, the user's privileges are restricted to a specific host, or set of hosts.
For example, you might have a user called superuser. If double-clicking on that username shows two subcategories, localhost and athena, this means that the user has a specific set of privileges if he/she connects from localhost, and a (probably different) set of privileges if he/she connects from athena.
Right-clicking on a username, or on one of the subcategories a user might have, provides access to the following commands:
Add a new User: Selecting this command adds a new user with the default name New User to the user list. You will have to fill in at least a username in the MySQL User field of the User Information tab, which, after applying this change, will also rename that user in the user accounts list.
Add a Host from which the User can connect: [SH] Mike: Remove "a" -> Add Host. Allows you to specify a host from which the user can connect. This command is unavailable if you right-click on a subcategory.
Remove Host from which the User can connect: Allows you to remove a host from which the user can connect. This command is unavailable unless you right-click on a subcategory.
Clone User: Makes a copy of the selected user, including all subcategories. The new user is called New User until you specify another name in the MySQL User field of the User Information tab. With that command, you can therefore create a user with identical privileges. [SH] Not yet implemented.
Delete User: Allows you to delete the selected user. You will be prompted to confirm that you really want to delete that user.
Refresh User List: Rereads the user list from the MySQL server. This is helpful when other users (on other connections) are editing user accounts. Note that selecting that command will collapse all subcategories.