Google offers many applications, including "built-in apps" which come with your Google Account like; Drive, Docs, Presentation, YouTube, Blogger, etc... and Chrome Apps & Extensions which you install (or your GAE admin installs) from the Chrome Web Store.
Find Your Google Apps from your browser (see below)
or you can also access them from your Chrome Apps Launcher
click on the new Google Apps Launcher
Chrome Web Store Apps for the Classroom
"The Chrome Web Store offers thousands of free and paid educational apps, tools, and extensions to help students and teachers make the most of their Chromebook. "
watch the following video...
then go to Chrome Apps & Extensions
select an app
example:How to Use Geogebra