When you complete quests or kill monsters you will be rewarded with experience. As you gain more experience, you will gradually increase in level. Gaining levels will allow you to fight more challenging monsters and explore more of the world.
The amount of experience that you have, as well as the amount needed to reach the next level, can be seen at the top left-hand corner of the interface. It will appear as a dark blue bar under your mana or energy bar.
As you complete quests and kill monsters you can accumulate fatigue whenever you accumulate normal experience. This fatigue can be turned into extra normal experience by visiting a Goblin Innkeeper and paying a small fee to rest.
The amount of fatigue that you can earn is limited, and once you earn the maximum amount you cannot earn any more. This maximum amount is increased the first time you log in every day, as well as by leveling up.
The amount of fatigue that you have earned, as well as the amount of fatigue that can still be earned, can be seen at the top left-hand corner of the interface. It will appear as a light blue bar under your mana or energy bar.