Many of the guilds provide specialised training to their memebers.

That training will either give some feats or allow you to advance in a prestige class.

See the guilds in the guild list to see what they train.

For each guild rank you can get one special training.

Special trainings are allways very expensive costing 1gp for the first one and then going up.

Many guilds allow you to get special feats as extra training as long as you have the prerequirisite feat.

In order to advance in a presige class, you need to unlock them by getting special training. The guilds provide this.