Computer networks serve several purposes. They can be used to share files instead of having to transfer them from one system to another using disks (know as a "sneaker net", due to the need to walk from one system to another). They can allow one printer, scanner or Internet connection to be shared by multiple systems. Large companies often use less powerful termal computers at employee desks that used shared software on a large server. This can reduce the costs of buying full computers as well as make securing systems and updating software easier. Computer networks can allow multiple people to collaborate on a single project, adding to a single document shared by a group of people.

Even if you only have one computer, you're connected to a network right now. The Internet is actually the world's largest computer network.

Networks can be either public or private. A group of computers inside a business usually are part of a private network (know as an INTRANET). This means only the machines inside the company can access other machines on the network. There is usually a single server or other networking device that allows them all to connect to public networks, like the Internet. This device (referred to as a PROXY) usually takes on the identity of the internal computer so the outside world won't be able to access it directly. The internal network is usually protected by a FIREWALL, which is a hardware or software device that blocks out unauthorized connections, such as from a hacker.

The internal private network is referred to as a LAN (Local Area Network), while the public network is known as a WAN (Wide Area Network). These two parts can work together to connect a group of computers both to each other and the Internet, but keep unwanted outsiders from connecting to the actual internal systems.