For the notion of tradition I need to say that "all the information for educational purpose".
To make use of that trick, you should able to connect to the LAN but cannot connect to internet since it is waiting to fill a authentication form that is not free to fill(generally, if it is free don't mass your mind).
We follow the process as, first look the LAN for other hosts' IP addresses. Find a good looking IP (luckily connected to internet already.). Then retrieve the MAC address of that IP by using ARP protocol. Set your MAC address to retrieved one. Check whether you can surf. If you can't, try another victim IP. Continue reading Simple hack to connect an authentication needed internet. (like in Starbucks)