It's a mini computer that you can use for programming etc. The reviews say you can do lots with it but don't say what! It's the size of a phone and you plug it in to your tv, and plug a keyboard and mouse in to the USB ports. It also connects to the internet with a network cable or you can buy a wireless dongle.
We got an SD card for ours, it allows the DCs to save their work. They mostly write simple programs on Scratch, or do command line programming. We've plugged ours into a HDMI socket on the TV, and use the keyboard from the computer.