The tours start from outside the HauptBahnhof, and in reality you need to pick it up here if you want a seat.
The tour runs with a live guide giving a full commentary in German, along with a pre-recorded multi-lingual commentary, however, only around half the seats have headphone sockets so there is a large chance that you don't get to hear the commentary
The tour takes in the major sights of the city, on both banks of the river.
The tour can either be done as a single circuit, or for a slightly higher charge your ticket becomes valid for two days to hop-on and off as you like