With this being something that seems like it would mostly appeal to absolute beginners, it might be better to instruct them to use the preloaded, nearly universally used file manager for a much easier time learning how it all works. The process is significantly simpler when uploading into the file manager. You're able to click upload, select the MyBB zipped file straight from your downloads, and then right click on it in the file manager to hit unzip. Then the unchanged steps about mysql would follow. This tutorial still works if you're willing to sit down and follow it precisely, though. Keep it up.