There are various relevant archive collections that you can search.
The first of these is the Europeana portal. Here you can discover tens of thousands of works of art, artifacts, books, videos and audios from all over Europe.
The German counterpart to this is the German Digital Library. Here you can find
"digitized holdings and indexing information from cultural and scientific institutions such as libraries, archives, museums, heritage offices, media libraries, universities and other research institutions. The DDB provides central access to digital images of books, documents and files, paintings, statues, installations, monuments, films and music."
(Source: Deutsche Digitale Bibliothek)
In the German Federal Archives you can search for digitized contemporary documents from the following periods:
- North German Confederation and German Reich
- Federal Republic of Germany with Western Allied occupation zones
- German Democratic Republic with Soviet occupation zone
Another relevant archive is the Political Archive of the Federal Foreign Office. Files on German foreign policy since 1867 are kept here. The holdings can be searched here: www.archiv.diplo.de/
Documents from the Stasi authorities can be found in the archives of the Office of the Federal Commissioner for the Records of the State Security Service of the former German Democratic Republic.
There are, of course, other state archives. You can find an overview on the pages of the Archivportal-D.
You can use the archive portal to view various archives from different archive sections in the individual federal states.