Roles are the equivalent of Windows NT/Windows 2000 groups. You create roles and then grant users membership to those roles. Users who are members of a role inherit the permissions assigned to that role. The process of creating roles and assigning permissions to those roles greatly facilitates the process of administering security. This is because, rather than having to assign specific rights to each user of a system, you can instead assign rights to groups of users.
SQL Server offers four types of roles. These include:
Fixed server roles
Fixed database roles
User-defined database roles
Each of these types of roles serves a specific purpose. Generally, you will use several types of roles in combination. ...