Here you can buy tickets for the event.
No, you don't have to. You can easily show the ticket on your smartphone. Help the organizer and pick up the ticket soon enough and set your display brightness to 100%, which makes the entrance even faster. If you have a very small or damaged display, print out your ticket for safety's sake.
The return of the tickets is not possible.
Of course, you can transfer the tickets to another person, but commercial resale is prohibited.