Look for Format in the editing menu, then find Fonts. This will provide a limited selection of fonts you can directly select.
If you want to try something not on that list, you will have to use the HTML editor. First identify the font you want to use. Then go to the HTML Editor and find the text you want to change. It will likely look this:
<p>Sample text</p>
You will want to edit it to be:
<p style="font-family: ENTER FONT NAME;">Sample text</p>
Note that not all fonts may be recognized so try to stick to common web fonts. Custom fonts usually don't work well.
