Data persistence help?

I realize this is not the place to ask for scripts. I do not understand how it works and I require a Data persistence with Levels and EXP. So every 100 EXP is a new level. Also I want a way to reward EXP and the amount of EXP awarded will be your a certain number (different for each thing) divided by your level. So for example 10/1 is 10 EXP however if you were level 2 you would only get 5. I also require a way to print the level in a GUI (Like Your level is:) Maybe using ..Player.Level Or something like that. Thanks in advance.