If you're used to Drupal 7, you might have a moment of frustration the first time you try to add a block to your pages in Drupal 8.
In Drupal 8, you won't see all your unused blocks stowed in the Disabled section of the Blocks page.
Instead, new blocks are hidden until you add them to a region using Drupal 8's new Place Block button:
Once you've used it a few times, your brain will switch over to the new way of doing things - but for Drupal 7 users who are new to Drupal 8, it can be a bit of an adjustment.