The Gnutella network is a peer-to-peer (P2P) network, which allows users on different networks to share files. However, each user still must connect to an "ultrapeer," which is a server that lists files shared by connected users. This makes it possible to search for files across hundreds or even thousands of other computers connected to the network.
Gnutella is a network protocol, not an actual program. Therefore, to access other computers on the Gnutella network, you must install a P2P program that supports Gnutella. Fortunately, many of these programs are available as shareware and can be downloaded from the Internet. Some popular Gnutella clients include Acquisition for the Mac and BearShare and Morpheus for Windows.