Work As Local Network Topologies.

Work As Local Network Topologies.
The primary function of a network (LAN or Local Area NetWork) is physically connecting multiple PCs to each other and also to a mainframe or minicomputer. This is accomplished through a wide variety of materials - cables braided, fiber optics, phone lines and even radio signals and infrared.

There are several ways of connecting PCs both physically and logically. Each network configuration - or topology - must still perform the same tasks. The most common situation in which a network faces is sending messages from a PC to another.
The message can be a request for data, a response request some other PC or an instruction to run a program that is stored on the network (the process in reality is somewhat more complex, see the topic How Does Communication Network).
The data or program that prompts the message may be stored in a PC used by a colleague networking,
on a file server or on a specific PC.
A file server is usually a high performance PC with big hard drive is not used exclusively by
any network user. It exists simply to meet all the other PCs in the network, providing a common place in
which are stored the data to be recovered with the maximum possible speed. Likewise, LAN servers may have Print usable by all network users. A print server is a PC connected to a printer, or then one intelligent printer that can be connected to a PC as a network with no bridge.

The network must receive requests for access through PCs - or we - connected to it, the network also needs to find a way to manage all these simultaneous requests for their services. Once the PC has the LAN services, it need to find a way to send message from one PC to another, so that the messages go only to the node trying to achieve and not for any other. In addition, the network needs to handle everything as fast as possible while distribute its service across all nodes.
Three network topologies - bus (bus), ring (token ring) and star (star) - account for most configurations
LAN.

Source: Evolution of Computers