Gnutella is a file sharing network that allows users to send and receive files over the Internet. The first part of its name comes from the GNU General Public License, which originally allowed the source of the program to be made available to the public. The second part of the name comes from Nutella, a chocolate hazelnut spread, which apparently the developers ate a lot of while working on the project.
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.