Instructions are in the game. WASD/arrows to move, if you go over the edge you have a few frames where you can still jump, this is a feature not a bug.
This platformer doesn't use any control blocks, no if/else, loops, waits, or clones. If you don't believe me then you can download the sb3 file and extract it, open project.json and search for "control_" (a block in the control category will have a opcode starting with "control_"). More details on how it was done is in this forum post: https://scratch.mit.edu/discuss/topic/656861
