One of the more useful things that can be done with networking services is sharing files via a network file system. The one usually used is called the Network File System, or NFS, developed by Sun.
With a network file system any file operations done by a program on one machine are sent over the network to another computer. This fools the program to think that all the files on the other computer are actually on the computer the program is running on. This makes information sharing extremely simple, since it requires no modifications to programs.