You allow a user to access a database by assigning a database username to the user's login ID. The username can be one created specifically for that login ID, or it can be someone else's username in the database (called an alias).
When you add a user to the database, you can also specify which group the user will belong to. A group is a collection of users and is a convenient way to provide common permissions to those users. There is a built-in group, called public, that users belong to by default.
A user who creates a database becomes the database owner (DBO) and has full privileges for that database. A user who creates a database object (for example, a table or a view) becomes the database object owner and has full privileges for that object.
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