Creating a simple leveling system

So I’ve been asked to make a simple leveling system (Similar to this: http://img3.fotos-hochladen.net/uploads/2015021300034kl9mxb086.jpg) where players gain 5 exp every 10 minutes.
Seems simple enough, but it also needs to be able to work with jobs in DarkRP where you need X amount of exp before you can play as that job/role.
I know enough to make it, I just have no idea where to start. Any tips?

Edit: Fixed the link, had the wrong thing coped.

Start making the lvl requirements possibly in table. That takes time to make it balanced. (For me atleast)

Idea took from blackmesa rp server, not?

As I’ve said, I’ve been asked to make it. I don’t care what the idea was taken from nor why the server owner wants it, I just make stuff for him. But as far as I can tell, it was from the BMRP server.

Maybe learning to code would be a good start.

Well, I just finished making it.
Sorry, you were saying?

Then why make the thread?

Because at the time of making the thread, I was unsure as to how I should start.
Guessed it, got it right, finished it.