Every student must re-register for the next semester during the current semester, i.e. they must inform the Student Office that they would like to continue studying in the next semester. This seems to be an unimportant formality, but it is nevertheless essential to do it, otherwise you could be exmatriculated in the worst case.
To re-register, you have to transfer the semester fee of (currently) 127 euros (student union fee + solidarity fee) within a set period of time and then you will receive the documents for the next semester in “MeinCampus” to print out. You should make a note of this period in your calendar and make sure you don’t miss it! Here (https://www.fau.eu/education/study-organisation/re-registration/) you can find further important information on the university website.
If you do miss the deadline for transferring the money, it’s not a disaster. Just take your semester fee in cash and any document that proves your identity (e.g. ID card) and walk to the Student Office (Halbmondstraße 6, attention: only open in the mornings!). Then hand in your fee at the payment office on the first floor and take your receipt to one of the counters on the ground floor, where you were when you enrolled. There you may have to deal with nasty looks or snarls from an annoyed student office staff member. So it’s better to remember this in good time and save yourself inconvenience!