A lan party is when you get a group of  people together with their PCs, And link them together so you can play against  each other in Multiplayer games.

For this you need a Network card Installing in your machine  (very cheap and easy to install) 

What happens then is that you plug a cable  into the Network card and the other end goes into a Hub (we supply the hub so don't worry about  that)

without going to Technical, put simply its  this.....

the fact that everyone in the room is  plugged into the hub all the computers are joined together like one.

You then all load the game on your machine  as normal and play the Lan (Local area network) option on the multiplayer games  option of the game. then once into the game all the enemy's in the game are not  computer controlled but are your mates in the same room.

A lot of people have tried something similar to this  by playing online, so yes it is similar but you don't suffer the same lag (jerkiness) that you sometimes get online.

the fun comes from shooting the person opposite you,  and you get to see the look on his face as he realizes it was you :-)