You didn't mention your SQLServer Version.
Use the following steps:
1) Open your
SqlServer Management Studio
> [
YOUR DATABASE
]>
Security
>
Roles
2) Right click over "
Database Roles
", select "
New Database Role
".
3)Click on "
Securables
" and select other database
roles
,
objects
, etc to be assigned to that role. After that click "OK." The database role should now appear in the "
Database Roles
" listing under
your database/security/roles
.
4)Assign permissions to
your database
role. Only assign permissions to the database role that are
absolutely necessary
.
For further information please visit
here
[UPDATED]
To Learn more about database role please visit the following links:
Database-Level Roles
Understanding SQL Server Roles
Creating User-Defined SQL Server Database Roles