In plain English
The yellow box must never trap you. Only drive in when you can drive straight out — except you may wait in the box to turn right while oncoming traffic clears.
Where you'll see it
Busy junctions and outside fire and ambulance stations, where a blocked junction would be serious.
The common trap
Forgetting the right-turn exception: you may sit in the box waiting to turn right. It's the only legal way to be stationary inside one.
Memory anchor
The box is lava — don't stand in it. Unless you're turning right, when you're allowed one careful step.