Wizard
The Wizard advance to the Warlock and Sorcerer. He uses a Spear as weapon. He got the lowest Damage in the end game but is still usefull for freezing stuff and tanking a lot. He uses freeze and shocks and with Critical Damage he still deals good Damage.
Dragonkin:Dragonkin classes start at level 1 but got a hero quests which gives them instant level 20. If you try to get to level 20 without the quest your character will just be bugged and won't be able to advance his class.
You need a Human class at level 20 to be able to create a Dragonkin.
Twin Fighter
The Twin Fighter advance to the Gemini, Mirage and Jumeaux. He uses Fists as weapon. He deals good damage in the start and the end of the game. He fights with two characters you can control at the same time using different skills. he can also use a skill called "Fusion" to "eat"
his Twin and fight as one person, that way he gain some new skills. He requires a lot of Skill points. He got himself a buff called "At Light Speed" this buff gives him 100% attackspeed and 150 Movementspeed. You shouldn't miss that.
Shaman
The Shaman advance to the Summoner, Elementalist and Earth Master. He uses a Gun Staff as weapon. He deals medium damage in the start but the highest Damage in the end of the game. He uses some summons which can fight with him and some other cool skills but his real damage come from his x-attack spam which gets boosted once he got the buff "Smart Shot" at 5/5. He focuses on Attackspeed and gaining more and more Magic Attack.
How to advance your class (level 20/40/60):The Purple quests are there to advance your class. There is a questchain at level 20/40 and 60. The quest for level 20 starts at Port of the Winds by Colin. After you finished that Purple quests you can go to your class Master who are next to the Sink Hole in Port of the Wins. The class Master of your class got two Hero(red) quests. Each of them will advance your job to one of those i mentioned above.
For the Job advancement for level 40 you need to go to Libra and talk with Pablo. For that questchain you need to kill 3 Monster which are located at the Wailing Hill, Nautilus Port and Mining Area. To Find them you have to go through the blue portals. Wailing Hill Bottom Left. Nautilus Port on the left, Mining Area Top Left corner.
For the Job advancement for level 60 you need to go to Vartika Hill and talk to Hell Krouzer. He will ask you to get him some stuff and then you have to clear Van Cliff which is located in the top of Village of Ash Mist.
Killing The Boss after Stage B25 can be hard for newcomer so feel free to ask for Help.