You can use Google Fonts in Showit and if you have a custom font you would like to use, you can use a service like Font Squirrel to create a .woff font file that you can upload to Showit and use for your design.
**Note: Be sure to add your converted .woff file to your media library, just as you would add an image. Only then will the custom font be available on the drop-down menu in the design settings. If needed - how to upload to your media library**
The following video walks you through that process: