Can view API doc in studio, but can't publish

Hello - Can anyone tell me what I’m doing wrong? I’m a tech writer new to Stoplight, and am working on personal demos for API documentation. As a Stoplight beginner, I’m lost in the UI and the docs have not helped. I read this page of your docs: When I follow this I get a Docs Not Found popup, and when I click Publish from Studio button, a blank screen is shown.

Generally I thought I could simply use an Open API spec file (YAML - have also tried a markdown file with the spec) to generate one-click documentation. I have connected my project to Github, and have tried a different project (same spec file) on the web only also, but still doesn’t work. Am I mistaken? Do I need to create a series of files with the content that will populate the published theme? (this wasn’t in the documentation…) . Thanks very much for any help.