In "Project Settings -> Project Structure" there are "pages" that explain the specific feature if you click on either of these header nodes:

• Modules
• Project Libraries
• Global Resources
• JDKs
• Global libraries
• Application server libraries

Usability would really be improved if you add buttons to each page, that let the user create a resource of the specific kind. E.g. a button "Add Module..." to the page that appears when you select "Modules". Currently there is a single, little "+" button that offers a ton of functionality and on the other hand there are detailed explanations with dedicated tree nodes but no functionality is offered there. (I just saw that there are context menu items on these tree nodes. Those "Add" entries are exactly those that should be available as buttons.)