For some events it is possible to book a place. Simple fill your informations in the form then confirm your registration via the receive email. Without confirmation the registration is not valid and will be freed so that other people can enjoy it.
Once your place is booked, you only have to come and pay for it at the beginning of the event. However, you need to come and pay at least 15 minutes before the start of the event, otherwise your registration will be canceled.