BAK: a stall is related to the angle of attack.
The aircraft will fly up to about 15 degrees angle of attack when it starts giving you messages.
In the circuit you'll be making Rate 1 turns (30 degrees bank) and the aircraft will turn smoothly on to the new heading.
If you decide to fly to the limit and make a Rate 2 turn (60 degrees and max for Rec Flying) the centreline if the aircraft is at 60 degrees, and [if you imagine, when the aircraft is on the ground there's a long steel rod through the canopy and hanging down below the aircraft with a big 2g weight ball hanging on the end] that big ball is pulling the aircraft outwards at 2 g, if you keep turning the angle of attack is now around 15 degrees - close to stall. If you pull in tighter at that throttle setting, you'll exceed 15 degrees and the nose will drop.
The most common areas for this to happen are when you overshoot the turn onto final, then pull the stick back to get there, and when your passenger pushes you for a better position to take photos.
Reinforcing that, if you observe the stick position at the stall, its always back in the same spot, pulling the elevators up fore more angle of attack.