Application and start of studies

What are the application deadlines for the Bachelor’s / Master’s programmes?
What happens at the start of the first semester?
How can I brush up my knowledge of maths prior to my studies?
I already have a degree. How can I get my prior learning accredited?
Should I really send my application documents by email and not by post?
Is a pre-study internship necessary or is this suspended because of the COVID-19 pandemic?