Where you have user accounts, you will find groups. Basically speaking, a group is a collection of user accounts. You might want to group all users who have administrative privileges into a group called Admins. Anyone who is a guest could be placed into a Guests group. You could also have groups for Email Users and Accountants. In this respect, an NT group is very similar to a traditional UNIX group.
The beauty of NT groups is that a user can be in multiple groups simultaneously. You could have an accountant with email access, so her account could be in both the Accountants and Email Users groups.
You need to know about two types of groups: global groups and local groups.
A global group can contain only user accounts ...