...
You will need a running Postgres server.
A quick web search will show you how to install one. You basically need a dedicated server running where everybody has access to. It’s also possible to host the database in the Cloud or at you web host.
Create new database
When you create a new library the software will automatically create the new database for you.
All you have to provide is the login information (user & password), the database server (server name or IP address) and the database name - how you want to call the new database (Example: das_element). The software will setup all the tables for you. Nothing that you have to do.
Optional: You can use a SSL certificate which is optional.