At the main train station there is an information point for those passing through Salzburg.
For those wishing to stay in Salzburg (or near Salzburg) there is an arrival center at the Messezentrum (the exact location can be found in the link below). There you will be registered by the Red Cross and accommodation is provided. There are food and drinks and facilities to shower. There is also psychological and legal assistance.
Arrival Center Salzburg