What is the difference between LAN and WAN??

I am well acquainted with LAN, it means local area network. I have LAN connection in my room so I understand how it works, but I have never used a WAN connection so I have no idea of it. At first please tell me the full meaning of the term WAN and how it is works? How was the connection developed? In LAN connection every PC has a particular IP address and the whole system needs not much care, as it is almost self dependent.
Does WAN works the same way? Do we require an internet connection for WAN? I can't figure out the working principle of WAN. Please someone explain what it is and how it works. The explanation should be as detailed as possible because detailed explanation can help me understand the real things. So be clear with the answer.
Thanks.
