The Block system in Drupal allows you to add arbitrary content into regions within a theme. A block could be as simple as just text or list content using Views.
In Drupal 7, the Block system is pretty limiting. For instance, a single block can only be assigned to a single region. You also have very basic control of hiding and displaying blocks.
In Drupal 8, the Block system has been revamped and it’s more flexible. The two big improvements: assign a single block to multiple regions and fieldable block types.
In this tutorial, we’ll continue work on our Drupal 8 blog site. We’ll add a static call-to-action which’ll only appear in the sidebar on the blog page. This call-to-action could be some promotional content or a newsletter sign-up form.
Then we’ll create a custom block type which we’ll use to create reusable promotional content that can be added to any blog post.