From Shaiya Wiki
To level up, you must gain a certain amount of experience points. You can gain experience points by killing mobs, other players and by doing quests.
To see how close you are to levelling up, look to the bottom-left of your screen. There will a bar displaying how much experience points you’ve collected so far in the form of a percent. If you want to see your experience points in more detail, press T or hover your mouse over the experience bar.
If you wish to see detailed information on how much experience points each level requires, pay the Difficulty Modes a visit.