When you join a network, think of it like checking in to a hotel. in your case you have a cable modem with one place to plug in a computer. that is basically a small hotel or a bed and breakfast. you plug one computer in, and the cable modem automatically assigns it a 'room' Once your computer is assigned a 'room' it knows where to send information from the internet. think of the information like mail or messages routed to your computer from the rest of the world. The problem, as you have discovered, is the cable modem only has one port, or place to plug in your computer. what you need is more ports. if you get a simple router, and plug it into the modem, the cable modem puts the router into its own 'room.' The router will have at least 4 places to plug in other computers (a larger hotel, hanging off a small hotel, which doesnt make much sense in terms of the analogy.). you will plug your two computers into the router and the router will route info between the internet and your computers.