You can buy the ESN Card at the ESN Office. At this office the board provides its services to students. At this office you can always ask you questions about ESN related things. You can also buy the tickets for the different activities organised at your office. If you want ot buy an ESN card you can do this here as well.
Just as with normal tickets sale, you have to buy the ESN Card during office hours. We will publish our office hours soon!