The P-events are the registration types that you defined in the Registration types/fees tab, see example below:
These are automatically regenerated as events and cannot be deleted. You can change the name, date, location and the maximum number of participants.
With PA-events you can indicate if an event is especially for accompanying persons. When the participant chooses a PA-event on the internet, he cannot finish the registration without filling in an accompanying person. If the participant doesn’t choose a PA-event, he cannot add an accompanying person.
An R-event can be a workshop, a lunch, a parking ticket, actually everything a participant can do/buy for your conference other then the registration fee (P-event).