Before a user can use a database, you must assign a username in that database to the user's login ID. The username can be the user's login ID, or it can be someone else's username in the database (called an alias). If you assign a user to a database with an alias, the user cannot access the database with any other username.
When you add a user to the database, you can also specify which group the user will belong to. By default, new users belong to the built-in public group. Users can be added to one other group.
Users who have been given access to a database still need permission to do things inside it. For information about setting up permissions, see Managing Object Permissions and Managing Statement Permissions.
For information about managing database users, choose one of the following topics:
Removing a User from a Database
Removing a Group from a Database