Loading Libraries into Drupal

Using Libraries API 2.x (as a module-developer)

 https://www.drupal.org/node/1342238

 

Installing an external library that is required by a contributed module

https://www.drupal.org/node/1440066

 

Loading PHP Libraries and Using Classes using Drupal Libraries module

http://stackoverflow.com/questions/19053676/loading-php-libraries-and-using-classes-using-drupal-libraries-module

  

Autoloading Classes

http://php.net/manual/en/language.oop5.autoload.php

 

3 Tips For Using External Libraries With Drupal

 http://engineeredweb.com/blog/10/5/3-tips-using-external-libraries-drupal/