H1 is used only in the "intro" section or banner/header section at the top of a page, and always is on top of an image.

Set the image for page by going to the settings (gear icon) for that page and adding a photo in the media tab. After you do that, you will be able to edit the text in the header like you would any other text on the page.

In general, the header text should be less than a sentence. Add two spacers above and two spacers below (without changing the height of them). If the header looks too tall after saving and viewing the live site with full width browser, remove one of the spacers.

h2 is used as the headline within the body of each page.

H3 is only used in the footer (the quotes are in H2). The footer has different color settings, which is why it looks different here.

Anything that is more than one sentence long should be considered body text and be in Normal.

and should be center, except when they're used as a "read more" or "back to" and should be size "small" and:

Blog thumbnails should be in the 3:2 aspect ratio