How do I change fonts and text size?

Open Settings › Appearance and scroll to Fonts and Display.

Checked against Terra 0.1.0

Choose Terra › Settings…, or press ⌘,.
Click Appearance and scroll to Fonts.
Type the name of a font on your Mac in UI font, Body font, Heading font or Monospace font. Leave a field blank to use the default.
Under Display, set UI font size, Body font size or Zoom.

Shortcut: none. ⌘, opens Settings.

Good to know

Changes apply right away. There is no save button.
Body text goes from 8 to 22 px, interface text from 11 to 18 px, and zoom from 70% to 150%.
These settings belong to the library that's open.
Spacing between lines is Line height, in Settings › Editor.