To mark a book as "read" click the check mark icon in the top right corner of the book (maybe this needs a more clear UI! 😅 ). It should turn green when you refresh the page after that, and show up in the "Read" tab in your library!

No importing from Goodreads yet, but some others have suggested it and I'm going to have to look into how they allow exporting and see what can be done! I agree that would be a hugely impactful feature!