This plugin works on the majority or WordPress installations without the need of an API key, however some server configurations prevent the plugin from reading the local fonts file bundled with the plugin. Either way I recommend taking the time to get an API key as it enables Automatic Background font updates in the Easy Google Fonts plugin.

Here is how to obtain a Free Google API Key:

Visit console.developers.google.com
Create a new project
Click APIs Under the APIs & auth menu
Turn on Web Fonts Developer API
Click Credentials under the APIs & auth menu
Create a new browser key and leave the referrer box empty
Copy and paste the google api key into the plugin admin screen (Log into your WordPress admin area, go to: Settings > Google Fonts and click the Advanced tab).