From the north (Nürnberg or Frankfurt), leave the autobahn at the Schwabing exit. From Stuttgart and the west, the autobahn ends at Obermenzing, Munich's most westerly suburb. The autobahns from Salzburg and the east, Garmisch and the south, and Lindau and the southwest all join the Mittlerer Ring (city beltway). When leaving any autobahn, follow the signs reading stadtmitte for downtown Munich.
Parking in Munich is nerve-racking and not cheap. There are several parking garages throughout the center, but your best bet is to use public transportation, which is exemplary.