What is the role of Active Directory (AD) and how can you Configure it?

When you install Windows Server on a computer, you can choose to configure a specific server role for that computer. When you want to create a new forest, a new domain, or an additional domain controller in an existing domain, you configure the server with the role of domain controller by installing AD DS.

By default, a domain controller stores one domain directory partition consisting of information about the domain in which it is located, plus the schema and configuration directory partitions for the entire forest. A domain controller that runs Windows Server 2008 R2, Windows Server 2008, or Windows Server 2003 can also store one or more application directory partitions. There are also specialized domain controller roles that perform specific functions in an AD DS environment. These specialized roles include global catalog servers and operations masters.

AD is the list of all users and their attributes, file permissions,usernames,pass, ....it's available on the Domain Controller Server and controls almost everything related to users.

Active Directory and its connexes services build the base of enterprise network  which work under windows operating system. As a result it has an effect  to backup informations concerning identity users, workstation and services in order to authenticate users or workstation and offer for them a proceeded Access  to enterprise ressources. the role can be configured by installing  the role Active Directory Domain Services under Windows Server Operating System.