Drupal 8 and Symfony

We all know that Symfony is already in the core of Drupal 8 but how it works and how both systems work? Not that many people understand fully this integration. Me neither but I would like to pubilsh my research notes about how Drupal 8 works now. Surely this material is based on the snapshot of beginning September and I really hope that more things will happen so this information is relevant only for some time.

I don't have any real life experience of the building projects with Symfony so my knowledge is very close to majority of drupal developers.

So lets start.