Use the arrow keys or touchscreen to move.
Thanks to @TheK1N9 for his project https://scratch.mit.edu/projects/14100981/. It has a much simpler platformer engine than most of the other ones I've seen. Also, thanks to @griffpatch_tutor for his tutorial at https://scratch.mit.edu/projects/67727504/. Even if I didn't use the same engine, his project helped me to understand what was going on and how platformer scripts work.
