Online Documentation for SQL Manager for SQL server
The Member Of tab of Login Editor allows you to define the login membership, i.e. to select the built-in server role(s) the login will belong to. The selected server roles determine the tasks that can be performed through the login.
To select a server role, you need to move it from the Available Server Roles list to the Selected Server Roles list. Use the buttons or drag-and-drop operations to move the server roles from one list to another.