In this example optional extras are available.

The staff attendees can bring one Guest at a reduced price

In this example there is a discounted rate which can only be purchased if the payers have the passcode (once they have logged in, they will need to enter a passcode in order to proceed with the booking for the discounted rate)

This event has an 'event' validation questionnaire attached which is designed to validate a customer's eligibility to book on an event prior to entering delegate details.  
This is achieved by asking the customer for a password which can be validated against a user list that has been uploaded into the system.   This kind of questionnaire is assigned at the over-all event level and should NOT include any response type questions as no data is saved at event level.

A customer response questionnaire can be added at Attendee category level to caputure any other data.

2 delegate rates and no extras or guests.

In this example, the event is full but payers can add themselves to a waiting list

NB:  The waiting list function only works when there is only one attendee category.  Do not use when more than one attendee category exists.