A class is essentially the selection of jobs you choose to pursue in Maple Story. As a Novice, you may not have a job yet. But with a lot of training, you will soon meet the requirement for your 1st job advancement. With new skills added after their job advancement, a novice should be able to level up quite rapidly.
The class Cygnus Knights is not under any category. The Aran class and the Evan class is under the Heroes category. Resistance has 3 jobs: Battle Mage, Wild Hunter and Mechanic. After Legend, Cannon Shooter,Mercedes, and Demon Slayer are introduced.