Drupal 8 is a big change to the popular CMS. If you plan to get started with Drupal 8 development, you should understand that under the hood it's a very different beast from Drupal 6 and 7, versions that are still in use commonly.
Every technical article you read on previous versions needs to be read with a grain of salt. Luckily the basic concepts of the system (view, content types, modules and more) remain the same, so if you're just getting started with Drupal you're in luck. You're on the same starting point with many more experienced Drupal developer.
Drupal relies heavily on contributed modules for creating functionalities. Due to the large technical changes in the latest version, many popular modules are not yet available for Drupal 8. Don't let this get you from getting started with it. If you're building a rather straightforward content driven site you'll likely do fine with the ones that are out there already.
If you're just getting started with Drupal, don't learn Drupal 7. Learn Drupal 8 and PHP programming in general, don't be too Drupal specific. Nowadays Drupal shares a lot with other PHP CMSes. Read up on these generic topics:
- Object Oriented Programming
- PHP Namespaces
- Dependency Injection
- Symfony Components
Once you have an idea about these, go forward and start playing around with a fresh install.
Here are some links to get you started: