You would need some sort of hub to set up the network and connect your different computers. (search for “router” on Amazon and you’ll get a ton) Some networks will connect with physical wires, some are wireless, it really depends on what types of connections your computers can make as to what will be easier.
Do your computers already share an internet connection? If so, they’re already connected and you would just need to create a workgroup (“homegroup” is the new Windows buzzword for it) and share your files. Usually there will be a “shared” directory under “My Documents” in Windows that is set up by default. You can also share folder by right clicking on them I believe (not sure if this is in all of the versions you have)
You might also look at a solution like Dropbox that basically just gives you a folder on each computer that has the same files in it and syncs up automatically as long as you have an internet connection. It’s free for a small account and you can take the files with you anywhere since they’re stored online.