Every kick in your track lands a drop on a sheet of glass, each at a new place, and the last few stay on the sheet. The snare, the mids, the highs and the low end keep them alive, so a passage with no kick holds its drops instead of going dark. Drop in a track, paste a link or open the mic; before any of that, a click lands a drop where you point.
Studio
Choose a track, or drop one anywhere on the page. Until then, a click lands a drop where you point.