There is a WiFi network on the aircraft that is usually turned on when you board. You connect to this like any other. When the aircraft is in the sky then it connects via satellite to the internet. You will see a window on the page that indicates that CBB is connected and you can logon. It's not super fast (maybe 500kbs?) but plenty fast for most things.

If you have a decent laptop that is less than 3 years old then you should have built-in wifi. If not then you can buy cards for about $50, I would guess. common brands are Netgear, D-link, Linksys, etc.