Video stills

There's all the ways people mentioned, but I think this one is the easiest. It only takes a picture of the video, not the whole screen.

When you are in whatever program you use to watch your videos, press "ctrl + alt + shift + print screen"

Then go to whatever graphic design program (MSPaint if you have nothing) you use, "Ctrl + V" or "edit => paste", save it and all done!