Something appears, you tap it, something else appears somewhere less convenient. That is the entire mechanic, and the game's only job is to make the gap between appearances shorter than your reaction time. It works on a phone as well as a keyboard, which the design was clearly built around.
It is a pure reflex score chase with a clean look and a very short distance between opening it and playing it. There is no progression to protect and nothing saved that you would miss, so a run costs nothing to abandon. Which is how it gets you into the fourth one.