The "festival" ticket allows access to the entertainment area, to access the festival's campsite you must add the complement "camping access" when you buy your ticket. 

And if you already have your ticket you can access the Buyer's Portal with your email and locator and add at any time the complements you need (Camping, Glamping, Plots, Cashless,...). If you prefer, you can add the Camping at the festival box office at your arrival.