A web page of solid body text is hard to scan for content structure and will not engage the eye. Adding display type to a document will provide landmarks to direct the reader through your content. Display type establishes an information structure and adds visual variety to draw the reader into your material. The key to effective display type is the careful and economic use of typographic emphasis.
There are time-honored typographical devices for adding emphasis to a block of text, but be sure to use them sparingly. If you make everything bold, then nothing will stand out and you will appear to be shouting at your readers. A good rule of thumb when working with type is to add emphasis using one parameter at a time. If you want to draw attention to the section heads in your document, don’t set them large, bold, and all uppercase. If you want them to be larger, increase their size by one measure. If you prefer bold, leave the heads the same size as your body text and make them bold. You will soon discover that only a small variation is required to establish visual contrast.