In Dream of Mirror Online, there are many jobs to choose from and you are not restricted to experiencing only one. There are 15 jobs in total. When you start, you begin as a Commoner and must reach level 10 in order to attempt the qualification quests for the other jobs.
To switch from one job to another, visit the Careers Advisor.
Each job has 2 active skill sets and a passive skill set that can be used to augment the capabilities of other jobs. They can be used provided that the requirements for the skills are met and the skill points to allow their usage have been spent on the respective job.
Each job progresses independently of the others. If a player levels up in one job, his or her levels in the other jobs remain as they were before. Attributes and skill point allotments pertain to only the active job: if you place points into Power in one job, it will not affect any of your attributes in any of your other jobs.
Note that this means you do not have to allot your commoner attribute points to match your future job!