All links are on this page.
Creating an image requires access to an operating system. After registering a team, the coach is granted rights to Microsoft store to download OS.
You will also need the scoring engine.
When making an image, plan what it is you want to test students on: specific area (users, security policies, program install/uninstall, overall practice...)
Map out the changes that you want to make. Maybe screenshot the scoring engine pages. Come up with a theme (latest movie, cartoon, etc.).
Create a base default image in VMWare. Save the image as multiple files. Make a copy and save for future changes.
According to your plan, make the changes to the image. Make a note of all the changes you perform to the image. Even small differences may come back to haunt you.
User Accounts can be tricky. If a new account is to be created, avoid 'whitespaces' (no spaces in the name) and avoid creating the user then deleting it.
Save your image and make a copy often. If you need to 'undo' something in the image, it is better not to have done it all.