With your semester student ID you can purchase the Studi ticket in the Seezeit-Shop at the university or in numerous kiosks in the city, e.g. in the underpass near the market square. It costs 53,20 euros and is valid one whole semester, i.e. six months. You can use the local commuter train “Seehas” (between central station Konstanz and the station Wollmatingen only), the ferry to Meersburg (as pedestrian or with your bike only), all Konstanz city bus lines, except the “Nachtschwärmer” nightbusses, and line 908 to Kreuzlingen.
Since winter semester 2012/13 you can also purchase the upgrade version: the VHB-Studi ticket. It costs 54,10 euros per semester and is valid in the whole VHB network of the Konstanz district (Verkehrsverbund Hegau-Bodensee).