First off, you need to clarify if you have a hub or a router. They are similar but you need a router to share the cable modem connection to the internet. A router will usually say so on the front something like "Cable/DSL Router".
Assuming that you do have a router (and it's not a wireless type), you should have from 2 to 5 outlets (typically). One is probably labeled "WAN" while the others are probably just numbered 1,2,3, and 4.
These outlets look very much like a telephone outlet but they are slightly different in size so don't get them mixed up.
First step is to turn off and unplug everything.
You want to connect a CAT 5 ethernet cable from the "WAN" connection to the ethernet connection on the cable modem.
Then you want to connect a CAT 5 ethernet cable from each computer (this assumes that it has an ethernet card installed or built in) to one of the numbered outlets. Doesn't matter which one goes where, they're all the same.
Once you have them connected, turn on (or plug in) the cable modem. Wait about 30 seconds then turn on (or plug in) the router. Now you can turn on each PC. If everything is correctly connected and the computers are configured properly, you should be able to go on the net.
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