If you are at this page, most likely you are participating on the CERN Open Days 2019 either as a speaker, performer or expert, yet you are not an alumni or part of a club.
For the purposes of the event you will be considered as an CONTRIBUTOR instead of a volunteer (Volunteers have a minimum shift to do and need to get trained prior to the event. In return they will receive t-shirt and food voucher. Contributors are exempt of training obligations but do not necessarily get the benefits either.)
Registration is mandatory to receive your Open Days specific name badge, without which you won’t be allowed to enter CERN premises on the days of the event. Although you are not a "volunteer" per se, please note that all information about access to CERN and other logistics can be found: http://cern.ch/od2019/volunteers