Chopping

I have a colleague that can do that... I know it is guiding the body of the knife with a knuckle, and point thumb inwards; Or control the point of the knife with the palm. I won't even try.

Keep one hand on the handle, and one hand on the top of the blade, but not the sharp part.
Another safe way is to use the knuckles on your left hand to guide the knife, keeping all your fingers angled AWAY from the blade, and use your right hand to do the chopping motion. You can reverse this second one if you're left-handed tho

I don`t think I`ll try that ! This is about my level.

right, I'm sticking with the tomato slicer and vegetable dicer.