Some themes will offer all nine formats, and others have fewer. Pick a format, add content to the post the way you normally so, and publish! Depending on your theme, you’ll see some stylistic differences between this post and your posts with the default Standard format.
If you start a new post containing a gallery, video, audio track, or quote, your theme may automatically apply the related post format. You can always choose “Standard” if you’d prefer the default layout.