You place the tip on a the glass (in normal use, on metal) and push. The
body moves down around 1/4" and then the stored energy is released into
the tip - hard enough to indent steel and more than enough to shatter
toughened glass.

https://www.youtube.com/watch?v=txh0lOVjN-E

https://www.youtube.com/watch?v=AdjAKTIYKtA

are a couple of American videos showing one working.