SQL Server Security

Authentication in SQL Server

SQL Server supports two authentication modes, Windows authentication mode (default) and mixed mode. 

SQL Server installs with a SQL Server login named sa (system administrator). It is not recommended to use sa login in your application. sa maps to sysadmin fixed server role. 

Server and Database roles in SQL Server

All versions of SQL Server uses role-based security. SQL server comes with set of fixed database roles. Within each database, SQL server has set of database roles. some of them are, 

You can find more about these in MSDN and MSSQL Tips article. You can also create custom schemas.

SQL Server Schemas

Allows more control over managing database object permissions. It is a named container for database objects. 

MSDN

http://stackoverflow.com/questions/1155120/sql-server-roles-schemas-users

Reference

Overview of SQL Server Security - MSDN