|You need a router with a WAN port|
Routers are available for Cable or ADSL broadband so you have to choose the right one.
You can get wired routers or wireless routers which also support usually 4 wired ports. I would recommend a wireless one for full flexibility.
Wireless routers come with different speed ratings e.g. 802.11a/b, 802.11b, 802.11g and 802.11n. a/b is the slowest and n is the fastest and latest. Get the 802.11n version if you can afford it.
You can connect your PCs to the router wirelessly or wired.
To connect in a wired way will require an RJ45 cable per PC of appropriate length (based on how far the PC will be from the router).
To connect wirelessly you will need a USB wireless adapter per PC. Ideally this should be the same 802.11 speed rating as the router or better as they tend to be back word compatible with slower speed routers. No ugly wires in this one.
Wired will give you the full speed of the interface.
Wireless will be marginally slower and it also depends on how far the PC is from the wireless router and any obstacles presented to the wireless signal including blind spots (due to the directionality of aerials).
Set up and connection instruction will come with the router. However, it is simple enough to do. Post back if you have difficulties doing so and someone will guide you.
Here are a few links for further reading:
☺ When everything else fails, read the instructions.