I hope that someone will be able to post more specific instructions than these, I don't have time at the moment to look up tutorials.
First you'll need to decide what you need. Is it a switch or a router? IF you want to just connect several computer together, it's a switch. f you want to connect your WiFi/wired network to Internet, you'll need a router.
Next are wired network cards. You'll need obviously enough ports for each cable. There are cards available with multiple ports, so they could be a good solution.
Next you'll need a WiFi card which can run as an access point (if you need that!). Here's a list of some cards that support that capabilities (I haven't used that company's product, so I can't comment if it's good or bad. Anyway, it's not necessary.). There's a technical term fot that capability, but I can't remember it at the moment. It's not the same as ability to make an Ad-Hoc network.
After that you'll need an OS which can be used as a router. Most popular are various GNU/Linux distributions, but it can be done with windows too.