Typically, you want something that will do all 3; b/g/n.
Most laptops have integrated 802.11 b/g/n wireless cards.
Check your network control panel to search for your network adapters.
Like Buwish said, it is dependant on your laptop model.
FYI: A router is a unit that splits one network point into multiple ports and a wireless access point. A wireless card or adapter is connected to a computer and can access the network provided by a router.