The two major differences: the VP9 is a striker-fired pistol, the P30SK V3 is a hammer-fired double-action/single action pistol; the P30SK is a sub-compact gun (the "full-size" P30 is comparable in size to the VP9). The different trigger systems lead to substantially different internal design and manual of arms.
Judging from the question, it would be useful for you to do some Googling for pictures, as well as for descriptions of the differences between striker and hammer-fired if that isn't clear to you.