Traveling from Salzberg to Lauterbrunnen

Look it up on either www.sbb.ch (Swiss Federal Railways), or www.oebb.at (Austrian Federal Railways).
One train every 2 hours, takes about 8½ hours, change at Zürich, Bern and Interlaken Ost. Just make sure you spell place names correctly: Salzburg.

What exactly is confusing you?

I think what might be confusing is that there is no great route by train to get you there quickly. We generally love taking trains and public transit in general in Europe, but knew that a rental car would be the best option for this area. We did this during a portion of our trip this past summer with a stop in Ruette. Found it best to rent a car in Freilassing (just across the German border 10 mins from Salzburg or so), drive to the Neuschwanstein Castle area and stayed in Ruette then drove to Lindau to return the car. This saved us rental fees for dropping off in a different country and allowed us to explore this amazing area. From Lindau, we took the train to Lucerne then on to Lauterbrunnen. Just an idea!

It looks like by train you need to plan 8-11 hours or so and driving directly would be 6-7 hours...
Have a wonderful trip! You are picking 2 amazing places!!! Be sure to check out Wengen when in Lauterbrunnen and tell the folks at Central Sports hello!

The other confusing factor "could" be that the OP is not using a national rail site and instead is using something like RailEurope to attempt train bookings.

Salzburg to Lauterbrunnen is, indeed, a good example of a route where options sold in Rail Europe's ticket sales database (focused on longer, faster trains) do not include many of the local and regional trains that will be reflected in a complete timetable from OEBB, SBB, or DB databases.

let's not forget the old-fashioned option - finding a Euro train travel agent expert and paying them for their services.

I agree with Phred. I have used EurAide and was well pleased. They can book trains all over Europe and have a representative in the US - Karen Murphy - 781-828-2488 - euraide.com. She will work with you on early purchase fares.
Barb

We did the opposite direction last fall - Lauterbrunnen (Murren) to Salzburg. All I did was go directly to the train station the day before we wanted to leave and the man selling me the tickets created the whole itinerary for me. With the exception of the enormous train station in Zurich, it was a breeze! Get off the train, walk two tracks over and get on another! Simple!