So you can buy a laptop with a wireless internet card in it - this means that it's ready to recieve a wireless signal. To get on the web though, you need to be near a station broadcasting a wireless signal. Usually this broadcast is achieved with a wireless router plugged into a DSL modem somewhere in your house/apartment area. The range on these things varies, sometimes people are able to steal their wireless connection from their neighbors (if it's not password protected) or places like Starbucks' or bookstores have them.
So if you have a wireless net enabled laptop and you are around a router broadcasting a wireless signal, you can expect to get internet.
hope that's enough to start