How do you break the glass on a fire alarm pull sstation?

The UK Fire Alarm says Break Gflass and there is a circle that says press here. Do you break the glas with your hand and then press the curcke or will pressing the cirlce break the glass? What will you feel when pressing the cirlce when the glass breaks? Will the glass fall on the floor? How do you get your hand out after the glass breaks? Do you neec to push a button after the glass breaks? How ard do you need to press