It's an external USB interface which provides you with 2 Focusrite pre-amps, Midi IO, a fairly comprehensive set of monitoring options and comes with 4 plugins from their Scarlett range.
Setup is an absolute breeze, the latency isn't super low, like down in the 4ms range, but it's perfectly useable and you get those Focusrite pre-amps which at this price level are difficult to beat.