Level
A characters level is based on their experience. With increasing level it needs more and more experience to reach the next level.
While a character progresses in the levels they unlock new game features
Rewards
Every time a character reaches a new level they get a reward. Stat and skill points are given every level, Stat points beginning from level 1 while the first Skill point is awarded for reaching level 10.
Stat points
With stat points you can increase the base stats of a character.
Skill points
With skill points you can level up the skills of a characters class