Currently, you can use the fonts available that appear above your canvas in the horizontal toolbar, but there's no way to add custom fonts. You can scroll through the fonts to see what's available. We've recently added over 50 new fonts in Fall 2017, so check 'em out!
Some of the fonts available do not have the bold and/or italic option, so if you wish to have use these options you'll need to scroll through the font list to see which fonts offer the ability to bold or italicize. We hope you enjoy the variety of Google fonts that we provide.
Dive into some great tips to pair your fonts here!