If you're curoius on how to create your own service class in a drupal 8 module, check out the article (only in German), part of the blog series on Drupal 8 module development I wrote for zensations.at.
Although so much has changed in the way modules are being created in Drupal 8, compared to the 7th version, there are so many similarities. It's just another (more modern and appreciated) way of doing it.
Recently I wrote an article for the blog of my employer dmcgroup.eu about the hotsauce changes we are happy to expect from the new 8th version of the beloved CMS Drupal. It is available only in German for now.