Free shipping within the United States uses the most economical shipping method available. In many cases it is USPS First Class mail without insurances or tracking. A postage stamp is added to small envelopes and items are considered delivered when accepted by the postal carrier. There is no way to determine where your package is or when you might actually receive it.
USA First Class Mail tracking service is available with weight limitations for less than $5. Contents are not insured but lost or delayed packages may be located. Other shipping options, like Priority Mail and FedEx, are available with insurance and tracking during checkout. For a higher nominal fee, international First Class Mail is available with tracking.