The guild is the starting area. It can be found near the spawn point.
It contains various Npcs, which are important for starting your own kingdom.
The guild is generated next to you, after you started the conquest.
When your kingship bar is half full, the guild will be attacked by dark warriors (?) and you have to defend it.
After the attack you need to give a stack of wood to the guild master and then click "fix the guild" in his menu.