This is what it's all about: Helping or leading your Guild to Victory in the Guild Wars, proving you belong to or own the most powerful guild in Parallel Universe. With the aid of your fellow Guild members, you will need to man up and defend your Guild Castle. You will need to make sure your guild has enough resources to survive and launch attacks on other Guild Castles by forming Regiments and invading them.

There is a catch though: Though you are generally considered a more powerful guild ally when you have an experienced character, your character cannot gain experience in the adventure world whilst playing the Guild War. So you will need to make sure your Guild is well defending before leaving your Castle and going exploring. 		 

The Guild Leader chooses where he wants to locate his Guild on the Guild War Map. You are then responsible for defending this Castle, by manning it with guild players and fortifying it with outer walls and War machines.
If defending isn't for you, you can form or join a Guild Regiment. This is a group of guild players intent on attacking enemy Guild Castles or battling enemy regiments. Regiments are essential if you wish to conquer enemy Guild Castles, though it far more risky than defending a Castle.
War Machines are a vital part of the Guild War. Castles cannot be defeated without a War Machine to knock them down, which is why Regiments need to contain War Machines in, should the Castle Walls be in tact. You will need to make the War Machines though, which takes a bit of time. Many hands make like work though and if several Guild members decide to make a War Machine, it will be produced quicker, especially if some of those guild members are Dwarves.
A Guild needs resources to function effectively. Your Regiments cannot attack or move through provinces without resources. The bigger the Regiment, the more resources they consume. A Guild Castle being attacked when low on resources is a lot weaker. Resources are produced by players. Some class/race combinations are better at producing certain resources than others.
Without effective spies you are blind to the enemies around you. The skill of your Intelligence system depends on the proportion of thieving characters you have in your guild. A good intelligence system will be able to tell you the strengths and weaknesses of enemy guilds.
Balance of your guild is everything. You need to juggle the type of characters you have in your guild to achieve a strong position in the Guild Wars. And you need to make sure your characters are doing the correct things in the Guild Wars. Timing too is important. If all your guild members are busy growing in the adventure game, your Castle will be very vulnerable.