It modifies the display of the cart and divides the purchase process into 2 steps. First, customers confirm the selection of products; second, they fill in contact details. In the second step, the shopping cart is displayed fullscreen.
It's handy when customers add many products to the cart: They won't need to scroll through the list of products to fill in the contact form in a pop-up. The form is now displayed on the left side of the screen and the shopping list on the right, so customers can see them simultaneously.
To enable this option, open the Settings tab of the block with a shopping cart and select the "Multi-step checkout" checkbox. Don't forget to re-publish pages to apply the changes.