Active directory allows an administrator to organize computers into containers called Organizational Units, or OUs. These OU containers are then used as discriminators to apply rules to the organization based upon their location in the structure. These rules are called Group Policy Objects , and they can do everything from decide who gets admin rights on which computer to what printers the computer can and cannot use.
We use system center to configure orders called Task Lists which are used to do things group policy cant as easily, like install and configure software and user accounts on a mass scale.
Of course, these aren't the only two options. However, these are the two Microsoft fronted options, and used in conjunction with each other and a well configured network, there is no business too large or order too complicated to be effectively administered to the entire network.