with a USB cable - it connects to one machine (doesn't matter which) for initial configuration purposes via the Ethernet cable supplied. Thereafter you may disconnect the cable and use all computers wirelessly if you wish, although you may also connect computers to the router via conventional Ethernet LAN cables - the router has four LAN ports at the back.
Each computer which you intend to use wirelessly must have a PCI or USB wireless network adapter or PCMIA card (in the case of a laptop) installed. If you aren't going to connect wirelessly then each machine must have a normal Ethernet network adapter. At least one machine must have that type of adapter anyway - so you can connect it to the router for setup purposes.
Don't hesitate to ask if you need more clarification, or if you need help with sharing the printer and scanner on a network.