The core Grav theme template (Antimatter) comes pre-configured to display two Google fonts downloaded from Google Fonts CDN. The two fonts used in the default configuration are: Montserrat (for all the header and display functions) and Raleway (for body text). Although these fonts are quite a nice combination, it is possible to over-ride these choices for a more individualistic look-and-feel.
There are two files that need to be adjusted:
Copy and paste the chunks of code on each of these pages so that the original code is saved intact. Comment-out the duplicate and insert the new font names into the proper areas of the un-commented copies.
The font combination that I've chosen for this site (as of March, 2016) is Oswald for headings and Droid Serif for body text.
By the way, a good site to use when choosing the ideal font combination is:
http://fontcdn.org/. Even thought its user interface is not as nice, another site to consider is