|Do you currently have cable internet service?|
You need a cable modem. If you don't currently own one then you will need to lease or buy. If you wish to use wireless connections for your laptop you will also need a wireless router.
I recommend using a router even if you only plan on using one wired connection. The router acts as a hardware firewall that protects your computer somewhat from the outside world.
Most wireless router will also have ports for connecting computers to it using a networking cable.