From Izanagi Online Wiki

Quests are tasks offered to players for them to complete to gain rewards: gold, exp, unlock a skill, or simply to progress the story of the game. The task can be in the form of kill quest, gathering, or errand quest. Quests are separated into 3 categories: Main Quests, Side Quests, and Repeatable Quests. Main Quests are related to the story of the game, so they are mandatory - while Side Quests and Repeatable Quests are optional.