Using headings properly can help in creating a semantic, organized structure to your content. If your page content has a lot of sections, each with its own subtitle, you should consider using "headings" instead of simply applying "Bold" or using CAPITAL LETTERS for your section titles.
Proper use of headings is an accessibility best practice. See "Use headings correctly to organize the structure of your content" from the "Top 10 Tips for Making Your Website Accessible" page on the Web Accessibility website for more information. Do not use headings purely for presentation, and do not skip heading levels.
If you like the "look and feel" of a particular heading, but the text you're adding does not need to be a heading, a Site Builder can use one of our optional HTML classes for paragraph styling. Similarly, if you like the "look and feel" of a particular heading but want to make sure you use the proper semantic heading structure (i.e., you like how a Heading 3 looks over a Heading 2 but do not want to skip heading levels), a Site Builder can use optional HTML classes for heading styling.
Applying a heading can be done via the expanded toolbar under the "Format" drop-down. If the formatting is unintentionally applied to more than just your section title, you may want to hit "Enter/Return" first to separate your section title from other content before applying the heading format. After you apply the format, you should be able to delete extra line/paragraph returns to close up any unwanted gaps.
NOTE: The "Heading 1" option is reserved for the title of the page, and is not available for use in the "Body" content of your pages.