Create an unversioned page
Create a normal versioned page, click the Versions Dropdown > Convert to Unversioned. You can also use this command to convert a versioned page into an unversioned page.
Convert an unversioned page into a versioned page
Open the unversioned page you want to convert, and click Edit. Click the version picker (which currently displays "unversioned"), and click Convert. Your page will be converted to the selected working version.