If you come from Germany, take the highway Munich-Salzburg until the highway Inntal, until Kufstein then go on through Kitzbühel, Mittersill, Kaprun and Zell am See.
Or you drive on the highway Munich Salzburg until the exit Inzell, then Lofer, Saalfelden untill Zell am See and Kaprun. For this variatino you need no austrian highway and no badge.
If you arrive from direction Vienna and you don't want to go through Germany, you can take the Tauernautobahn until Bischofshofen and then until Zell am See and Kaprun.