Category Discount or Surcharge Modul

[LightBlue82]

It is my understanding that I can see here all the groups and groups discount or surcharge information. this helps me to create groups with different procentage on discounts to different artikles and brands.
I have a few questions to this module:

- How and where do i set these discounts? (it wont let me add categorie discounts in the groups individually and when i change the numbers here in this module, it doesnt save any of the changes. it lets me change any value that i would like, but doesnt save it)

- Why do i have this modul twice with slight differences?

1)

2)

this confuses me a little