Like the title said i’m kinda confused how the classes
example :
( i took one example from other forums sorry if it’s not allowed )
what does “rank” means ?
why we can become the “same” classes again in different rank ?
p/s i might ask more question if there’s a reply 
“Rank” is the position you are in after progressing from your first class choice (Swordsman/Archer/Wizard/Cleric). For example:
[Rank 1] Cleric
[Rank 2] Priest
[Rank 3] Bokor
You can also choose to become the same class again (You can currently do this up to 2 times per class) to strengthen your current skills and unlock new ones. For example:
[Rank 1] Cleric
[Rank 2] Priest
[Rank 3] Priest 2
[Rank 4] Priest 3
[Rank 5] Monk
Here’s a skill simulator so you can have a better grasp of it:
You start out as Rank 1 class.
The four Rank 1 classes are Swordy, Mage, Archer and Cleric.
Everytime you get to choose a new class, your rank increases by 1.
At every new rank, there are always 2 new classes to choose from and additionally the 3rd option of re-picking your current class.
Everytime you re-pick a class, the circle of that class increases by 1.
Let’s say you pick an Archer as your Rank 1 class.
Once you are ready to class change, you get the 2 new class options: Ranger and Quarrel Shooter to choose from. Additionally you get the choice of the class you are currently at, the Archer.
So in total you are left with 3 classes to choose from for your Rank 2 class:
Archer, Ranger, Quarrel Shooter.
If you pick Ranger as your Rank 2 class, your class would be referred to as:
Archer C1, Ranger C1, since you picked both archer and ranger once and their circles are still at one.
If you pick Archer for a second time at Rank 2, your class would be referred to as:
Archer C2, since you are now in the Archer’s second circle.
But no matter which class you would choose here, your class Rank would be 2.
Choosing the same class repeatedly and hence increasing it’s circle will increase the level cap of that classes skills and unlock new skills for that class.
There is a maximum of 3 circles for every class, so you can not choose the same class more than 3 times.
Hope that helps.
i thought you said you can go to the class 2 times only ?
or is the 1st advancement is not counted ?
when is this “rank” appeared ?
is there a “Quest” for every advancement ?
There is a Quest for every advancement. Every 15 class levels you get to pick a new class/or continue on the one you are. Each class can go to circle 3 (Original choice plus 2 upgrades).
I believe when you get the pop up for a new Rank you can pick your choice there and it directs you to the quest giver for it.
Like Sixaxis said check out http://www.tosbase.com/tools/skill-simulator/
And it will all make sense easier to see it.
is the “class levels” is different from character levels ?
That is correct. Check out this youtube video for an example.
You will see the guy has a Character level of 33 and class level of 10. When you gain a Character level you get a stat point to use and when you get a class level you get a point to put into your class skills.
thanks a lot 
now i understand a more how the game works