If you're new to Germany, likely or not you'll be travelling with public transport.
S-Bahn or Trams, and Deutsche Bahn, or trains. Of course, busses too, but I'm less familiar with them.
Despite what things look like on the outside, the Deutsche Bahn is not the modern up-to-date service it appears to be. It is likely the first place you will learn about the German concept of "Kundigungsfrist".
Most places in Germany will have an option to cancel a subscription, but you must do it six weeks, and they will be extreme calendar weeks - they are counting every day, before a contract ends or begins.
In the case of Deutsche Bahn, this will apply to Germany Tickets, and BahnKarte.
Do not be fooled - they aren't trying to make your life easier, they are trying to trap you into contracts you do not want.
The Bahnkarte is a predatory system whereby if you fail to cancel on time, you will be locked into a full year of continued service. There are often situations where the explanation or situation for the Bahnkarte is not adequately explained, or you are not properly informed before the Kundigungsfrist that you can and should cancel. Cancellation options will be difficult to find (hidden in small sub-menus in the app, and buried online or requiring a mountain of paperwork).
Simply put, the Deutsche Bahn likes to offer the ProbeBahnkarte to you when you book a ticket (often making your tickets significantly cheaper even including the cost of the ProbeBahnkarte) and trapping you into a huge cost later on.
My best advice - DO NOT PROCURE A BAHNKARTE!!!
Should you find yourself in the situation where you do get yourself into a Bahnkarte siutation this information (in German) may provide useful:
https://www.kanzlei-hollweck.de/ratgeber/db-bahncard/
It also includes example letters you can send Deutsche Bahn.
Good luck!