Recently Drupal 8 has gone under many changes due to which students are facing some difficulties to find some of functionalities.
You can browse to link below if you want to know what are the changes that have been taken place between various drupal versions. It gives you entire list of functions and variables that have been removed or renamed from version to version.
List of changes @ https://drupal.org/list-changes
If you are new to drupal and are looking for module development you might find this video perfect for you. This video explains how to get started by developing a basic module in drupal-8 and explains changes that drupal has gone from drupal 7 to drupal 8.
Module development @ https://www.youtube.com/watch?v=Q-aubgnL72s
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I found these slides helpful
I found these slides helpful - https://dl.dropboxusercontent.com/u/10160/Upgrading%20Modules%20to%20Dru...