As you are in the wireless forum, you presumably have a wireless router and you want to know about adding a wireless adapter.
If your laptop has a suitable slot I would add a PC Card (used to be PCMCIA) wifi adapter but USB versions are more common and are universally supported.
If your router is n wireless I would choose an n capable wireless adapter and preferably of the same brand as the router.
Most of what you need to know beyond that should be contained in your router's manual.