Go to the kiosk right away to get a ticket--if it is crowded, your entry ticket might be for a later time (tours start every 15 minutes). You will give up your belongings at wardrobe and change into a miner's outfit--pretty goofy. Then, when it is time, you will get on a train that takes you deep into the mountain. Guides speak German, but English and other language information is available from "virtual" tour guides at each stop. The highlights are two long slides, which take you down a couple of stories but are really fun!! The first one has a camera set up halfway down, so smile pretty! And if you like the pic, you can purchase it when you leave.
http://www.salzwelt.de/salzbergwerk-berchtesgaden/en/default.asp