You can find information about your computer science degree program or non-faculty computer science degree program as well as all information about your mathematics degree program and non-faculty mathematics degree program on the official pages of the university. There you will also find a "Guide" as a PDF where everything is described in detail.
The secretariat is in the department itself, at Spiegelgasse 1 on the 5th floor.
To enrol for a lecture, you must select the "Enrol" option in the services and then enrol for the desired lectures in the course catalog. To do this, you first add them to the watch list and as soon as you have definitely decided on a selection, you can transfer the watch list. You can check what you have already taken at any time in the services. Please note that you can only register for lectures within the registration period. You can find more information here
You will need a laptop or tablet for your mathematics or computer science studies in order to download learning content from ADAM, edit it or submit exercises online. In addition, there are some areas, especially in computer science studies but also occasionally in math studies, where it is mandatory to work with a laptop.
A tablet with a pen is not absolutely necessary, but highly recommended to always have your notes with you digitally. Mathematical formulas or small sketches in particular are rather awkward to write on a laptop with a keyboard and mouse... If you don't want to do this, you can of course continue to work with paper.
Project Neptun is offering laptops and tablets for students at low prices at the start of each semester.