Haha those are my photos! Forgot I had that placeholder in there. I'll remove it until I have a tutorial video in place - that's my last major task left, outside some bug fixes and waiting for Chrome to fix their audio.
As for how the site works - make sure you have a microphone and ideally headphones. Click START and you'll hear a metronome. Click ADD TRACK to record a loop. If you're musically inclined you can combine multiple recordings to make a short looping song, by either adding bars to a loop or layering multiple tracks. Hit CTRL or right-click (long press on mobile) a track to modify how it sounds or delete it.
I'll post it to Show HN hopefully soon.