The flight into Salzburg from Frankfurt is easy, although Frankfurt is a large and cumbersome airport.
You can fly into Munich and then take the train to Salzburg, which is ~1.5 hrs. Harder logistically to arrange passage and find the train.
You can fly into Vienna and then take the train to Salzburg, which is ~2.5 hrs. Easier logistically to arrange passage and find the train.
Once you get off the plane you can take either a cab or the bus. If you take a cab it will cost you about 15-20 Euros to get to the Congress Center. If you take the bus you will need a ticket. They are inexpensive, and can be purchased in the magazine shop (General Store) inside the airport. Ask for a bus ticket. It is less than 2 Euros. Then you will want to get on the #2 bus headed to town (going right, if your back is to the airport). Even if you get on the #2 bus going the other direction it makes a fairly quick loop back. It will take about 20 minutes before you pass the train station. Soon after that (2-4 minutes) the Congress Center will be on the right.
Salzburg Congress Center
Auerspergstraße 6 - 5020 Salzburg, AUSTRIA
Tel. 0043662 88987-0