The airport is a bit far from the city center but you can take the S-Bahn train from Flughafen Munchen to Marienplatz in about 30 minutes. From there, you can easily walk around the old town and see the New Town Hall, the Frauenkirche, the Viktualienmarkt, Odeansplatz, maybe climb to the top of Alter Peter for a great view of the city, stop by the Hofbrauhaus for a real tourist experience, visit the English garden.