According to the membership rules:
"Crash Helmet, Boots, Gloves and Long-sleeved shirt/jacket MUST BE WORN while practising on the Site"
That being said, especially as a new rider or if you have prior injuries, rocks are hard and having a bit of armour can increase your confidence. You're less likely to be worried about falling off if you are a little bit protected.
Protective gear usually ranges from trials bottoms/trousers which are generally quite stretchy with some slightly padded bits (knees, thighs) to lightweight motocross armour. There's also potentially torso protection, thigh/tailbone protection, possibly leg/knee protection depending on your preference.
Riders generally wear trials boots which come up to about mid-calf and are reasonably protective whilst being more flexible than motocross boots. Slipping off the pedals is fairly common and shin/calves are easily punctured by the pedal teeth or squished between bike and obstacle so good protection there is advisable. The boots tend to also have a bit of tread so you're not slipping around at the first sign of things getting a bit muddy.
You'll need to find the balance between protection and freedom of movement that you personally are comfortable with and this will vary based on age, experience, prior injuries, how bold you're planning to be and how prone you are to falling off.
The same goes for helmets - a trials helmet usually doesn't have the front part (lower face protection) that motocross helmets do, which gives you better visibility, but for those of us who are prone to landing face first that might not be enough, so use whatever you're most comfortable with :-)