Free shipping is only offered for destinations within the contiguous United States. It is not available for addresses in Alaska, Hawaii, and other US territories such as Puerto Rico and Guam.
Upon checkout, you will see an option for free USPS First Class Mail in your choice of shipping methods.
If you do not see the option to click on FREE First Class Shipping, it means that the order is not eligible for free shipping due to its weight or the destination of the package. First Class Mail can only be used on packages that are under 16oz.