To display discounted price and percentage, Go to "Product Class/Price" then input the price/value on the "Old Price" from the "New Price".
Ex:
Old price is 100
New Price is 50
Upon uploading or adding product to your shop, click on the "Product Class/Price".
Next, click on "Add Product Class" then input a price/value on the "New Price"
For discounts, input the price/value on the "Old Price" from the "New Price"