If there is a large amount of text (over 750 characters) then headers make it much easier for all users to navigate through the content. You can see how to apply a heading in RadEditor in the Apply Paragraph Styles section in RadEditor's End User Manual, e.g.
Predefined paragraph styles are used to ease the process of formatting paragraphs. The user can apply consistent paragraph styles to a document. The predefined styles include different heading styles, and other styles defined by the developer. To apply a paragraph style to some text, first place the cursor within the text, then from the paragraph styles dropdown list, select the style you want to apply.
More information about heading is available at: http://www.w3.org/TR/WCAG20-TECHS/H42.