There backstory of rappelz is quite an interesting one, it tells of how the world had nothing on it but monsters and animals, then one day, the beings of light and darkness came together to bring upon the world, man.
Humans were very primitive and the divine beings of light and darkness helped them become the prosperous race that they later became, then the beings left, but not before leaving behind their offspring to watch over the humans to make sure nothing goes wrong, for 500 years, they lived in harmony and to this day, that kinship was never severed. The decendants of Light were known as the Deva, 'Wingless Angels'.
The humans named themselves the Gaia, 'Hammer of Earth', and the decendants of darkness were known as the Asura, 'Hornless Devils'. They lived together and war was never between them and the game does not take place after a severance of their kinship, they still live peacefully with eachother, therefore if you find a race not of your own, don't kill it XP. Each race has 'variations' of the 4 classes available to you. The Warrior, the Mage, the Priest and the Rogue. Warrior use heavy armor and large weapons to win their battle, mages utilize the mana of the world to use powerful spells of pure special effects brilliance, the Priest is the support class and is almost never seen outside a party but can still hold their own while flying solo, the Rogue is naturally the speed character who like shitting hard and fast rather strong and slow.
Each of the 3 races have different 'versions' of these classes, and each version have special powers exclusive to the races version, therfore you need to pick carefully who you going to be and what class you will be once you've picked you optimal race. For example, I'm a an Asura, and the warrior class is what I am, but a warrior is considered a 'Strider' when your an Asura. They don't have alot of muscle and therefore utilize a bit of magic to defeat monsters. With that, I will leave the choosing to you.