To use Amazon Cash, a customer gets a barcode from Amazon, which is accessible either via text message or by printing it out. They can take that barcode to a participating store, show the cashier the barcode. and give them money. The cashier adds that cash to your Amazon balance.
Participating stores currently include CVS Pharmacy, Speedway, Sheetz, Kum & Go, D&W Fresh Market, Family Fare Supermarkets, and VG's Grocery.
The service is free to use, and single transactions must be between $15 and $500. The funds should be available immediately, and Amazon sends you a confirmation notification via email, text, or with a push notification, if you have Amazon mobile app notifications enabled.
While Apple CEO Tim Cook has said services like Apple Pay are going to "kill cash" (see the video below), a portion of the US still relies on cash. As TechCrunch noted, data from the FDIC indicated that 9 million households in 2015 were "unbanked," meaning that no one in the household had a checking or savings account. Another nearly 24.5 million households were "underbanked."