The text on your site -- blog entries you post, product descriptions you write, the checkout form, and so on -- are displayed using a consistent font. You can change which fonts are used by using the Fonts section on the Basics tab of the Design page (Design > Basics).
Changing Your Site Fonts
You can choose a different font for your headers and titles, and for the normal text on your site. When you change a font using the dropdown selectors, the sample text to the right will change to give you a preview of what the text on your site will look like.
Click Save configuration at the bottom of the page to make your changes take effect.