Arrival/departure: Please book your own train ticket using your BahnCard. For this trip, it even pays off to buy a BahnCard, see here especially for the "Probe BahnCards". Make sure to arrive by Monday evening, 29/05. The lectures start on Tuesday, 30/05 at 9am and end on Friday at 5pm.
You can arrive earlier e.g. to spend the long Pentecost weekend in the Geneva region, or depart later if you like. You are responsible for booking your additional nights in the CERN hostel (if there is space) or anywhere else.