It's pretty simple: an audio clip plays, and you're asked to identify which language the clip is in. It starts off with two choices per clip, and as you get more right, more options will appear. Difficulty is a bit random, thanks to the algorithm that generates language choices; one of the languages I got wrong was Slovak, when my four options were Slovak, two other Slavic languages I also don't know, and Khmer (the only thing I knew for sure was that it wasn't Khmer).
I am pleased that I was able to correctly identify Thai and Lao, though. Not bad for a white American whose non-native languages tend towards the spotty at best.