You can manage your databases using phpMyAdmin, a tool that allows you to manage MySQL databases using a web browser. To access phpMyAdmin, find your database in the control panel by clicking More Services from the top menu and then selecting Databases. Click the name of database you wish to manage or edit from the list and then click the link next to Browse database manager.
Following this link should log you straight into the database. If you wish to add another user, simply click the Users link on the top of that database page.
This will show you a list of all current database users. To add another click Add New User.