Hello,
In order to choose type of product to be shown set in the drop-down: http://prntscr.com/jihzwo as written in the previous response.

All products – means all existing products.
Featured products – find here how to configure featured product https://docs.woocommerce.com/document/managing-products/

In order to set the Sale Product your need to add sales price to product.

Newly added product would be displayed if you set New label product

Best sellers = products most often sold they are not configured

List of ID product which your want to show by ID, find here how to get ID https://docs.woocommerce.com/document/managing-products/

Best Regards