Important: Discounts cannot be set from the main Products page. They must be applied within a Presentation in Tile View. Editing a Product's starting price will change it everywhere.
Manually Discount a Product
Open a Presentation and make sure you are viewing your products in Tile View.
Click a product's price to bring up a popup and type in the new discounted price. In this example, you would click on "50.00 USD".
Click away from the pop-up or hit Enter to close the box. Then click the Save button to save the changes to your Presentation.
This is how a discounted price will look to your buyer - with the discounted price in red and a slash through the original price.
Set a Percentage Discount for a Group of Products
See the article "Apply a Discount to a Section"