The Schengen area in the European Union forms a uniform area of security and law. The objective of the Schengen Treaty from 1985 is the complete elimination of all personal controls at the interior borders of the signatory states.
This is why the inspection of a valid border-crossing document at the interior borders has been discontinued. However, valid personal documents proving your identity must be carried with you and presented upon request. Everyone must go through an identity check at the borders of the Schengen area with other countries and present a border-crossing document (passport or personal identity card as appropriate for origin and destination).
The immigration points have been separated into EU/Schengen and Non-Schengen as a way to expedite the inspections.
Go to the website of the German Foreign Office to find out what countries belong to the Schengen area: