With Turbo, enable price savings for the Product page, Cart page, and Mini cart to show both the Price and Compare at price for your products.
Put products on sale by setting their Price lower than the Compare at price in the Products admin.
Price Savings on the Product Page
Open Products, then Default product with the page selector.
In the left sidebar, click the toggle beside Product information to reveal the blocks.
Click to open the Price block, then enable Show price savings to display how much your customer is saving (both percentage and price amount).
Price Savings on the Cart Page
Click the cart icon or use the page selector to open the Cart page template.
Open Cart page in the left sidebar, then enable the Show total savings setting.
Product Savings in the Mini Cart
Open the Theme settings, then Cart. Below Mini cart, enable Show total savings.