You are the snake that gets longer with every dot eaten. You will also get faster as you get longer. 1. Use the arrow keys to move 2. Collect the coloured dot 3. Don't run into the edges, walls or yourself
Kinda funny - I watched this vid AFTER I'd made my game and this guy encounters all the same issues I did. He's obviously not doing it in Scratch but his and my process were very similar. Mine took me a lot longer though.