The main point of the game is to play out your character in one of twelve different Lifes, all of which are unlocked from the beginning of the game. Each one specializes in one of three key areas, which are combat, gathering and crafting. You are also able to freely switch your Life to another by visiting the Guild Office in a town, allowing you to perform many possible tasks at once.
For example, you start out as a Hunter, which is a combat class, and decide to switch to a Blacksmith, a crafting class. You can switch back to Hunter and still create items as a Blacksmith. Each Life has a list of Challenges associated with them, which when completed and reported to the respective master, will allow that Life to level up.
The level up requirement (stars) for each Life is different and will be listed on each Life's page. Also, as you level them up, you will each bonus stats that are only available when you are using that particular Life. For example, a Fledgling Mercenary gets HP +10 and Strength +2, but if you switch to another Life, you will lose those stats.