There are different font properties, which could be changed in the SiteBuilder's editor. They include:
Controls for editing the aforementioned properties are shown on the figure below.
The mechanism of changing the formatting is standard - first you type your text and after typing you select a sentence or a paragraph or an individual word and then change some element of the formatting via the described controls. For example, making it bold.
All the font editing controls are obvious except the template field. There you can select between number of readily available styles which you can apply to different portions of your document. It is a good idea to use them throughout your document for consistency.