Using Reminders App

I am using macOS Catalina version 10.15.2 and am trying to start to use the Reminders App. But I just do not seem to understand the logic of the system and am totally failing to get it to work. I have googled for help, but none of the articles I have found seem to relate to the version of the App that I have on my machine.

Surely it cannot be that difficult. Can anyone point me to an up-to-date manual on how to use Reminders?