|You usually use a router. You can buy a wireless router which would require thet each pc/laptop is fitted with a wireless adapter card, most laptops come with a card build in whereas most desktops do not. |
You can also buy a wired router(non-wireless) which is essentially the same thing as a wireless one although it connects to the pcs/laptops by an ethernet cable.
BUT on most wireless routers you can actually connect them to the pcs/laptops using a cable as well as wirelessly. Not all wireless router allow both wireless and cables connections.
So you probably ideally want to buy a wireless router that has a 4 port switch(cables connections) built in.
There are a lot of models out there, but netgear and linksys are very good brands.