title: How does OOP manage to 'include' classes stored in different files
body: <p>I'm trying to move into OOP development and am turning to here as I'm sick of searching the web and finding only the very basic information about what classes are and how they can inherit from each other - <em>that</em> I understand.</p>
  
  <p>What I don't understand as yet is how all these classes can be stored in different files, doted around a folder structure, and yet all you need to do to use the class is just mention its name in your code. How does this work exactly? </p>
  
  <p>And on a related note, if anyone can recommend a good book or online tutorial which will provide a good foundation in OOP (preferably php based) I'd be very grateful.</p>