There are various types. The main one is CAT5 or ethernet. There are also more advanced situations which may use fiber optics. Obviously, you also need to use power cords to power the equipment you use for networking.
To connect a computer to a modem you would typically use and ethernet cable. You can use a use cable if you have the usb drivers for the modem, though ethernet is a much faster and more reliable connection.
Wow, that is a big question. It all depends on how many different computer and extra (i.e printers, etc) you have hooked up to your network. A good rule of thumb is two cables for every device
