How to add a library in Intellij Idea

I recently switched from Eclipse to Intellij. Now I'm trying to use the andengine library.

In Eclipse it was easy to add libraries. Just right click > properties > add library.

In Intellij there is no option when you right click a folder (see image). How can I add a project library (a folder, not a jar file) in Intellij?

Thank you..

Navigate to File > Project Structure, select Modules, and hit the plus button to add another folder (with source code).