A network is a system that allows multiple computers to share resources. For example, there can be a file server on a network, such that a user will be able to access the files stored on the file server from any computer connected to the network. There are two network types that are more common than others: Ethernet and Token Ring.
Ethernet is by far the most common network type. In a simple sense, the way it works is that all of the computers in a network are connected to a hub (a box which connects network cards together). When a computer has "something to say," or more technically, sends a packet, it announces the packet and the destination. When the hub receives a packet, it makes a copy of the packet and sends it to all other computers connected to the hub. The computer holding the IP address to which the packet was being sent to (i.e. the destination) takes the packet. In a nutshell, this is what happens. Going into more detail is beyond the scope of this site.
Token Ring is a technology which is in some cases more efficient than the Ethernet method, but is much more expensive. Nowadays, most LANs (Local Area Network) are based on Ethernet rather than token ring. Thus we will not try to attempt to explain how token ring networks work. However, if you would like to learn more about the details of Token Ring networks, you can take a look at patent #5053946, which describes Token Ring networks in ample detail.
Network cards connect the computer to the network. Everything that the computer does that has to do with sending packets over the network goes through the computer's network card (and subsequently through one or more hubs, and then to the receiving computer's network card). If you are buying a network card, make sure that it will be compatible with your already established LAN. If you are setting up a new LAN, we would recommend to use a 100Mbps setup, as this is the fastest affordable setup.
To show you what a network involves, we have taken pictures of the hub cabinet (the place where all the hubs are stored) at our high school. The first one is a view seen from the front, the other one from the back. All the cables come in through the floor into the back of the cabinet, and connect to the hubs in the front.
