Product Discount Method:
You can select between rate or amount method.

Groups discount:
This discount is applied for each product.
Leave empty if no group discount should be applied (default setting).
Example with rate method: Indicate 0.1 for 10% discounts on every product.

Custom discount by product:
If you need to have a custom discount by product, you can set the value in product’s page “Groups pricing” tab.
Leave empty if this product doesn’t need a custom discount (default value will be used).