There is a mediator in each guild waiting for you to take on quests.
If the mediator has no quests for you, try raising your fame level to 30.
ex) if it is a maritime guild raise battle fame up to 30.
Taking on quests
Select a quest that fits you best. Higher fame will gain you access to even more quests.
Completing a quest
Read the quest information carefully before setting out to accomplish it.
If the quest proves to be too difficult press the cancel button.
Once you have completed your quest report back to the mediator at the guild to claim your reward. In some cities female workers at the tavern can report on your behalf if you buy them a drink. This is a good option if you are too far away from the city to report yourself.