Before you start trying to set up a computer network, try and get yourself a basic understanding of what networking actually means.  This will provide you with: networking rules; how and where to start; and a very easy to follow approach to establish everything you need to get there.

Once you have understood the basics of networking, you are ready to begin.  Check out the different types of networks available and then decide which one will work best for you and your company.  You could go for a simple network (just between a few colleagues) or one that uses a computer and some kind of server.  This decision will depend on how many computers you want tied to the network.

Once the computers and servers are connected, check out cable related issues, whether or not you need a hub, and if there are any physical limitations based on where the computer and other equipment is located.  Also check out the different network cards.  Ensure you understand about all the different components also before purchasing any of them.