Folder structure

I followed the tutorial on how to make a extra. But if a want to add a new class to that extra. Where do I place it in the folder structure?

core
- components
-- NAME
--- elements
--- model
---- CLASS
---- CLASS2
or

core
- components
-- NAME
--- elements
--- model
---- CLASS
----- CLASS.class.php
--CLASS2
--- elements
--- model
---- CLASS2
----- CLASS2.class.php

Take a look at another major extra, Quip. Its class files are all in core/components/quip/model/quip.

https://github.com/splittingred/Quip/tree/develop/core/components/quip/model/quip

In fact, splittingred's github repositories are all excellent examples to browse through and learn from.

https://github.com/splittingred

That's the standard location -- it allows you to call addPackage() and it's kin to load the classes.

You might also look at the MyComponent/getMyComponent package and the tutorial here: http://bobsguides.com/mycomponent-tutorial.html