In Drupal 7, it's possible to group fields for a content type with fieldsets, vertical tabs and so on.
Where are this options in Drupal 8? I didn't find something in the Manage fields or Manage form display tab.
That functionality is provided by the Field Group module.
Fieldgroup will, as the name implies, group fields together. All fieldable entities will have the possibility to add groups to wrap their fields together. Fieldgroup comes with default HTML wrappers like vertical tabs, horizontal tabs, accordions, fieldsets or div wrappers.
There is a Drupal 8 version available.