So I've just uploaded my Openrocket walkthru/getting started guide document to git. It's the script that we follow as a part of my rocket design workshops I've run a few times now. I've also shared this document a to a few people directly who have worked through it successfully in about 20 minutes. It takes you through designing and simulating a small model rocket but you'll be able to experiment with your own larger and more amazing designs by the end of it!
Feel free to share far and wide.