Product discount
In the products page click on the second icon at the right side of the desired product too apply a discount to this product.
A window will pop up whth 3 discount mode options and a field where you'll type the discount value.
Modes:
Percent
Here you can type a value between 0 and 100. That will be the percentage taken of the product's current price.
Here if the product's price is $100 and you type a value of 20, the new price will be L$80.
Flat
In flat mode the typed value will be subtracted from the product's current price.
As an example, if the produt's current price is $100 and you type a value of 10, the product's price will be L$90.
Override
In this mode the typed value will be applied as the current product price.
So, if the product's current price is $100 and you type a value of 40 in override mode, the product's price will be now L$40.