NIS stands for Network Information Services, and will let you (if properly set up) have user accounts be stored on one central machine and then those people can login as themselves to every machine on the network. It avoids, for instance, the problem where someone has logins on tons of machines and won't change their password because they don't want to have to login to each machine to do it separately.

Which is cool, but useless for you since you don't have a home network, nor do you have any need to centrally manage user logins. Even after you have a home network, you'll likely have few enough accounts and machines that it is OK to handle it manually.

Cheers,
Ben