Need help with editor for custom race

[Kyuhunter]

I am trying to make a custom race, from the DanD wiki. I am currently trying to make a racial special ability that adds a weapon. The damage die of the weapon increases every few levels from a d4 up to a d12.
I know that an eval script is probably the way to go, but i have no experience with those so far.

If someone could show me how it is done and explain me how it works it would be greatly appreciated. If there already is a guide somewhere it would be nice if you could link it for me.

Thanks in advance!
Kyuhunter