Just press the arrow key that matches the one on screen.
Viewing post in Sisyphus Up The Hill jam comments
I see. When I load the game, the instruction dialog is still showing and that is obscuring the arrows. It goes away only when I die after 2-3 key presses. [update: I realized clicking on one of the Roman numerals cleared the box. I'm assuming those are difficulty levels? There should be instructions to choose one with the mouse.]