Guild halls are created by dedicating a tower using the guild command. A noble cannot dedicate a guild hall until he has met all the requirements to join the guild, i.e., he must have learned all the non-guild skills. He must also be alone in the tower when he dedicates it. Guilds can only be created in a city, and only one guild of a particular type can be built in a city.
Some guilds also have other features.
For example, the Trading guild hall has a market where special trade goods are bought and sold. In some games, guild halls teach the base skill. To use a guild hall as a source of teaching, a noble will have to be escorted into the guild hall as part of a guild member's stack.