In Blood Feud: Rohan Online, a great deal of time is spent leveling your character. There are currently 110 levels in the game. Accordingly there are monsters with levels ranging from 1 to 110 and possibly higher. Most of your time is spent slaying monsters and clearing the world of Rohan from evil creatures unleashed by the gods.
It is recommended you fight monsters your own level, but there isn't much stopping you from entering a high-leveled area and testing your luck. In some cases you may be successful. In others you may be lacking the defense, armor and levels needed to survive in the area.
Monsters more than 10 levels beneath you will not grant you any experience, while monsters more than 10 levels above you will grant less experience than they would grant someone of a higher level. However, higher level monsters grant more experience in general, so it is important to find a balance.