This is the back-office of LCA - Leibniz's Correspondents and Acquaintances Project.
From these pages you can access structured data, reach the Mediawiki pages, where you can add texts about Correspondents' biography and bibliography, and the Website pages, where part of the information stored in the back-end is shown in a graphical view.
You are using an instance of Wikibase, the software developed by the Wikimedia Foundation for the management of structured data of Wikidata.
For general documentation on how to use the Wikibase software, you can look at the Wikidata Help portal.
The LCA project implements only part of the features offered by Wikibase, as it is documented in these pages.