This is a regular cooking pot such as you might bring with you on a camping trip. Attached is a USB cable. The pot thermoelectrically converts excess heat into power which can then be used to charge various and sundry gadgets, like your phone or tablet.
It won’t be as fast as using a wall charger, of course; an iPhone should take about 3-5 hours to charge via this device. Certainly not your ideal primary charger, but in a pinch it’ll do nicely.
Another thing to note is that it is apparently safe for use over open flames, though of course you’ll want to be careful of where the cable gets draped.