Enter a title in the small box, paste Markdown or HTML into the large box, then press Convert to save a file suitable for importing into GitBook.
Headings are promoted a level, so Heading 2 becomes Heading 1. Note: if importing HTML rather than Markdown, GitBook incorrectly imports both Heading 1 and Heading 2 as Heading 2, so you'll have to fix any Heading 1s manually after the import.
GitBook doesn't support <kbd> tags for keyboard shortcuts, so these are converted to inline code.