Site Discounts put a category, a catalog, or your whole inventory on sale on your website — the discounted price shows on the item pages automatically for the period you choose. Find the tool under Website › Marketing › Site Discounts.
Creating a discount
Click Add and choose a scope (a category/catalog, or site-wide). On the form, pick the Category/Catalog, set the Discount percentage, and optionally: exclude items over or under a price, limit it to items added between two dates, and set a Minimum sale amount (a price floor the discount will not go below). Add Start and End dates if it should run for a limited time, then Save — eligible items begin showing the sale price.
Editing a discount
On the Site Discounts list, click the Edit icon on the discount's row, adjust, and save. Delete removes it and returns those items to full price.
Which items are eligible: a discount applies to every eligible item in its scope unless the item's Allow Discount toggle is off — turn that off on net-priced books you never want discounted (see Editing item fields). And note a site discount changes the displayed price for everyone; if you want a code customers enter at checkout instead, that is a coupon.