Samsung Pay not only supports the NFC payment method found in iOS and Android devices, but also supports MST. This means you can use it just about anywhere you swipe a card in the US.
The promise of mobile payments has been held back by carriers, retail outlets, and technology. Thanks to Samsung's adoption of MST and NFC, you can now pay with your phone almost anywhere you can swipe or tap your credit card.
I've been paying for products using Samsung Pay on my Galaxy Note 5 for a month thanks to early access to the beta program. Yesterday, an update appeared on my Note 5 as Samsung rolled out full support for Samsung Pay.
Samsung Pay is now available for anyone in the US with a Samsung Galaxy Note 5, Galaxy S6 Edge+, Galaxy S6 Edge, or Galaxy S6. Your phone has to be running on Sprint, AT&T, T-Mobile, or US Cellular. Verizon still doesn't accept Samsung Pay.
While I can use my Bank of America credit card, USAA Federal Savings Bank's debit card is not yet supported. MasterCard and Visa are supported, along with Bank of America, Citi, and US Bank. Given that USAA was one of the first to offer mobile payment support, I imagine we will see this bank and many others added soon.
In addition to the convenience of paying for goods with your phone, Samsung also has a Samsung Pay promotion where you can choose to receive a free wallet flip cover or wireless charging pad (not the fast charge one) after you setup a qualifying card.