Answer:
Munich's Franz Josef Strauss International Airport ("Flughafen München") is 28 km north-east of Munich and connected by rail every 10 minutes (S1 and S8) to the main train station "Hauptbahnhof", a 43 minute ride.
Tip: Less walking, a bus leaves to the Hauptbahnhof every 30 minutes right outside each terminal only a few meters from exiting customs. The S-bahn is 300-600 meters away.