Static stretching is hold one stretch for a stated amount of time, say 15 seconds.
PNF stretches require someone to assist you. For example if ou were doing a hamstring PNF stretch you would be lying on your back with one leg raised as high as you can whilst keepingnit straight. This would be held for 10 seconds then you would use your hams to push against your helper for 10. Once a muscle has been contracted it goes into relaxation which would allow your helper to stretch it further. This process would be repeated 3 times. Hard to explain briefly but hope this helps!!