Report Builder can use almost any web font you have access to. The Choose Font dialog comes with a pre-selected set of fonts from fonts.google.com (use the drop-down button/list on the right hand side). You can also type in the name of a font into the box – if this font is available via fonts.google.com Report Builder will automatically link to it and use it in your report (try typing Orbitron into the box and see what happens!).
You can also use one of the standard fonts found on most computer systems (for example Arial is available on almost every windows system, but it’s not very pretty) or use one the standard font keywords – sans-serif, serif, monospace – to leave the final font choice up to the browser.
If you want to use a font not available on fonts.google.com you will need to first add an @import rule to the CSS for your report via the Advanced Styling dialog, then just type the name of that font into the box.