User accounts in Active Directory give people and programs the access to resources in a windows domain. These accounts are used to allow people to access resources, manage the access users have to resources like files and directories and allow programs to be able to run in a particular context. According to this, the answer is that the two main functions of user accounts in Active Directory are: allow users to access resources and method for user authentication to the network.
An in AD, a user account consists of all the information that includes user names, passwords, and groups. All these information defines a domain user in which a user account has membership access to. With the advanced features of Kerbos, mutual authentication in user accounts to a service is achieved.
