cilpolir wrote:First google everything, and if you have specific questions, come back here
That question seemed pretty specific to me.
@OP - everyone on your network has a MAC Address - it's basically a unique identifier for that device connecting to the network. Networks that require you to pay to be on them or log how much data you transfer will use your mac address to identify you.
Let's say you're guest A, and there is another guest B on your hotel network. You have to pay $10 a day in order to get on your network. He's already paid, but you haven't. To get your internet for free, all you have to do is change (spoof) your mac address to his. The network will think you are him and thus have already paid and let you go on.
Regarding actually doing this, a program like kismet