train from munich airport to garmisch

A little punctuation would make this post much easier to read. But anyway...

There's no direct train to GaP. You take an Sbahn to Munich-Pasing and then a Regiobahn to GaP.

It's best to buy any ticket from the machine (I don't even know if there is a desk at the airport stations). Neither Bayern Tickets nor individual tickets are train-specific for this route, so you can take any train all day.

The S-Bahn (S1) from the airport does not go through Pasing. It enters the main S-Bahn line at Laim, one station closer to the Hbf than Pasing. If you want to catch the train to Garmisch-Partenkirchen at Pasing, you would have to get off at Laim and take the next S-Bahn to Pasing. According to the Bahn website, the recommended route is to go in to the Hbf and catch the train from there. Getting to the train from the S-Bahn in Pasing is probably simpler than at the Hbf, but requires the additional connection in Laim. Either way you get to Garmisch-P at the same time.

If you change at the Hbf, you'll come into the deep (Tief) S-Bahn station. Go up one level from the tracks and proceed in the opposite direction to what the S-Bahn came in) until you see signs for tracks 27-36. Follow them to the Starnburger wing station.

There is a DB counter upstairs in the Munich Airport Center (MAC), but certain tickets will be 2€ more expensive over the counter vs from the automat on the station platform. The least expensive ticket that will get you to Garmisch-Partenkirchen is the Werdenfels-Ticket see here for covered trains for 19€ (from the automat, 21€ from the counter) for one person, 23€ for two).

This webpage from the Bahn shows how to use the ticket automat to get the Werdenfels-Ticket (it's in German but pretty self-explanatory). It shows the screens you will see on an automat in Bavaria. The screen on the upper left corner is the opening screen on the automat.

Enter the querie for a Sunday, when the poster is arriving. Munich-Pasing is the only option that shows up on the Deutche Bahn website from now until July.

EDIT: Wait, some of the Sunday queuries I'm entering also show more complicated connections, but just about all of them go through the Pasing station at some point.

All of the routes to Garmisch go through Pasing, but the S1 itself does not.

If you take the S-8 around the east end of town and come in through Munich Ostbahnhof, you'll eventually go to Pasing, and you can catch the train there, but that route takes longer than taking the S1 to the Hbf and catching the train to Garmisch from there. Also, the Pasing station is outside, with only a covering over the platforms - sheltered from the rain but not the cold. Most of the change at the Hbf will be indoors.

By the way, the sign at the airport shows the S1 going to Ostbahnhof and the S8 going to Geltendorf (or another station west of town depending on time of day). Those are the final destinations. The S1 comes into Munich at Laim, goes through the Hbf and ends at Ostbahnhof. The S8 comes into Munich at Ost, goes through the Hbf, Laim, and Pasing, then on.

I was looking at the schedule for this coming Sunday (you didn't give a date). It looks like the schedule changes in a week for weekends, due, I think, to the construction of the new tunnel under Munich.

On weekends, most S-Bahn go non-stop from Ost to the Hbf (no stops under Munich, like at Marienplatz). S8 goes non-stop from Ost all the way to Pasing and gets to Pasing 9 minutes earlier than it does this Sunday. You'll have 13 min to change in Pasing from the S8 to the train to Garmisch. The S1 still comes all the way in to the Hbf from the airport, so you can change at the Hbf.