Utilizing private methods/vars inside module I'm creating a custom module which uses a few hooks and then after the form is submitted it will dive into custom PHP interaction that interfaces with an external restful API. 

I want some of these variables and functions to be private as they will contain business rules and some variables that I wouldn't want someone to get their hands on (easily).

I'm uncertain of how to do this in Drupal. I understand that I would need to create a PHP class which would then have private/public methods available inside of it. But how do I do this? 

Do I build this PHP class in its own file outside of my .module file and then use files[] = includes/MyClass.class.php in my .info file to import this external class file in?

Then once it's successfully imported in I could instantiate it with $something = new MyClass();?

Is it that simple to do, or is there another/better way?
Yes - it's that simple. Remember; Drupal is only PHP.

Although your class should be called MyClass.php rather than MyClass.class.php to adhere to the Drupal Coding Standards for OO code (note - this isn't explicitly declared, but is hinted at when they describe the Interface file naming conventions).

Just to pad this out a bit; you could also use the X Autoload module to allow for PSR-4 style autoloading instead of adding your class in the files[] array. I do this for as much D7 code as possible now (where I'm not using Composer Manager), and would whole heartedly recommend it.


  xautoload is a comprehensive and yet highly efficient PHP class
  loading suite.
  
  Most importantly, it provides Drupal-8-style PSR-4 (and the old D8
  PSR-0-style in "lib") autoloading for Drupal 7. But it is also a great
  tool for 3rd party autoloading.