You can choose a Google Font or a Websafe font from the list, write the exact name of a System Font or Upload a custom font file.
It's a tool to test and analyze webfonts that you intend to use in your websites or projects.
You can compare fonts from different sources (Google Fonts, System Fonts or any font file downloaded from internet), analyze their x-height, weights, characteristics and peculiarities, and display their legibility at different sizes.
Its' not a tool to discover new fonts: web has plenty of these tools and another one is not necessary. Use Google Font, Font Squirrel or simply search on Google.
Install webfont|test app for chrome for a quick access!