Video is made up of a lot of still pictures called frames. For NTSC video
there are 30 frames in one second. Do you know which frame do you want to
get as a picture file?
In Windows Movie Maker, bring the video into Collections area by selecting
Import Video or drag and drop from Windows Explorer directly. Click on the
video and play it in the Preview screen on the right. At the frame position
you want to capture press Pause. Now use the "Snapshot" button under the
preview screen to safe the current frame as a picture file.