Drill four 5/8-in.-dia. 1/2-in.-deep holes on the large disc?inside the traced circle?then use 5/8-in. dowel centers to transfer the hole locations to the underside of the small disc. Drill four 1/2-in.-deep holes on the underside of the small disc and a 1/2-in.-deep hole in the center of the top for the dowel handle. Glue in the dowels to join the discs, and glue in the handle. We drilled a wood ball for a handle knob, but a screw-on ceramic knob also provides a comfortable, attractive grip.
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.)