R9SCARRY,
You may be referring to the lever on the frame, behind the trigger... That is the cocking lever. Although the P9S can be fired in double action mode, the cocker allows you to fire in single action mode after a depression on the lever with your thumb. To decock, you apply the safety -- then pull the trigger.
It is definitely a right hander's gun, unlike HK's later creation -- the P7, which is a lefty's dream (at least it is for me). Like the P7, the fixed barrel and polygonal bore makes the P9S extemely accurate.
My German police surplus P9S was not in near as good of shape finish-wise, compared to Cuteo's (I'm jealous). So, mine is off to A.R.S for refinish in HK black.