Roles are a lot like Windows—they allow you to assign permissions to a group of users easily and they can have built-in permissions (implicit permissions) that cannot be changed. Two types of roles are available:
Server roles. Applied at the server level
Database roles. Applied at the database level
You use server roles to grant server administration capabilities. If you make a login a member of a role, users who use this login can perform any tasks permitted by the role. For example, members of the sysadmin role have the highest level of permissions on SQL Server and can perform any type of task.
You set server roles at the server level, and you predefine them. This means that these permissions affect the entire server and you cannot ...