There are three ways to offer free shipping. The first method is a bit sneaky and involves simply adding the shipping cost into the price of the products, which might not always help meet customer expectations.
The second method is to offer a minimum spend threshold to encourage customers to spend more on your products to receive the free shipments offer. This method can make customers spend a bit more than they intended to get the offer, and thus increase your bottom line.
The third method is to simply eat the shipping cost yourself in the hope that the offer will increase sales and your profit margin enough to make it worthwhile.