I don't understand exactly what we are turning in for the problem sets. Is there a webpage that tells us exactly what the assignments are? e.g. For the Scratch problem set, are we simply supposed to turn in a Scratch program? And how do we do that?
There is a detailed explanation of what and how to do for all the problem sets, yes there are separate web pages for each pset and even for hacker edition (you don't get credits for solving hacker edition problems). Here is list of all those pages, however it should not be too difficult for you to find them separately on edX. If you are new to edX, then try considering the course edX Demo.