AS above answer. There are regular trains. Its worth knowing at the moment the whole of Germany, their government are giving all travellers including tourist a 7 euro ticket per person to travel by bus tram and train can purchase from Munich train station. We bought our tickets before travel from the UK and it costed us more as we didn't know.

the main train station Munche Hbf which is about 2 km (1.2 mi) from Marienplatz. You can go to Train Line for info regarding trains from Munich Hbf to Garmisch