Many things must happen for a user to gain access into a network. First, the network must be accessible. For security reasons, some networks will close themselves to or limit outside contact. These are called firewalls . Second, the user must have a means of contacting the network.
Accounts allow the server to control which and how many users have access to the server's resources.
This ability to gain access to different networks and different resources is the true power of networking. At OSU, we have hundreds of networks running simultaneously. Many run Novell, some run UNIX, and with the advent of Windows 95, some are running Microsoft.