At the Castle Guild you can choose to participate in a variety of quests/missions. The missions are given out by the Guildmaster Vilnar. At anyone one time, you may have two missions, one from the category Mission and the other from the category Main Mission. Those which come from the category Mission are more like side quests. They are not essential to the main storyline, though completing them is not by any means a hassle since they generally coincide with the direction of the Main Mission anyway. Those quests which come out of the Main Mission pertain to the advancement of the main storyline.
There are two types of Missions which someone might undertake: Combat Missions and Find Missions. Combat missions involve hunting down various monsters and slaying them. For example, vanquishing 3 Gremlins. Find Missions involve traveling to a location and retrieving an object, normally indicated by an exclamation mark inside a blue hex field.
After completing a Mission or Main Mission, one must return to the Castle in order to receive the reward. One must be careful not to die after completing the requirements of a Mission, otherwise all Mission progress is lost.
A Sky Racer Compass can be used to return to the castle safely and quickly, especially when low on health. It is not suggested to use it otherwise because there are warp portals that return you to the castle on each map.