Need Clarification on Project Directories

I'm using Laravel. The "App" directory contains all models and controllers. The Resoures directory contains all the views. Public contains css and js.

I don't understand what specifiying the Directories does to PHPStorm - how does it help me ?

Also I do nto understand what a "content root" really is. All 3 ? or is it just the top level project directory ?

Many thanks !!