Begin by cutting off a 10-in. length of the board and setting it aside. Rip the remaining 38-in. board to 6 in. wide and cut five evenly spaced saw kerfs 5/8 in. deep along one face. Crosscut the slotted board into four 9-in. pieces and glue them into a block, being careful not to slop glue into the saw kerfs (you can clean them out with a knife before the glue dries). Saw a 15-degree angle on one end and screw the plywood piece under the angled end of the block.
But, there’s nothing wrong with showing people what’s possible if they work their butts off. Too many people expect immediate success when they start an online woodworking channel or website. It truly has to be your passion in order for someone to be successful in it. If they’re only doing YouTube or online stuff expecting to get rich quick or even to earn a little bit of income, I believe they’re in it for the wrong reasons and will get burned out quickly.
You can also use Google image search to research a project. Unlike the PDF search, the image search provides a photo of what the project will look like, which is helpful in determining if you want to pursue building it. By doing an image search for how to build a step stool, you will have a ton of options that all lead to woodworking plans of various quality. (The how to part of these is important—otherwise you’ll just get pictures of step stools.)