StrategyWiki has more information about MapleStory Jobs
New players are sent to Maple Island, a floating island specifically designed to be beginner-friendly. Unlike many other MMORPGs, players in MapleStory cannot choose a job when they create a character. Rather, every character starts with the job Beginner until they meet the requirements to complete the first job advancement.

At either level eight or ten, depending on the desired class, the player can willingly choose to complete the first job advancement and acquire a new class as a Warrior, Magician, Bowman, Thief, or Pirate (though Pirates are only available in KoreaMS). The Magician class is the only class that can be chosen at level eight. Further class progression is only allowed within the scope of the first class advancement chosen. There are either three or four class advancements available (depending on what version the user plays) as the player progresses through the game. Some players, however, decide to not get a job and become "permanent Beginners." Permanent Beginners may chose to leave Maple Island but those that decide not to are referred to as "Islanders".