LAN's take many different shapes, they require each PC computer to have a network interface card, and they generally follow IEEE standards for communications and infrastructure. The topology of a LAN is just its physical arrangement or shape. The bulk of topologies used today are star, bus and token ring. Star topology means that the arrangement of the LAN resembles a star. A star LAN has a central hub or computer from which each computer on the network is directly connected.
Bus topology means that the arrangement resembles the seating on a bus.
Token Ring means the computers are arranged in a ring. They communicate by passing an electronic token from computer to computer. Each computer on the network needs an expansion card to interface to the network. The network card merely sends and receives information over the network. Take a look at the netcard I brought.