Video = Combination of Pictures, a picture = a frame. A shutter speed, determine how fast every picture is exposed to light. A 30fps Video with shutter speed of 1/60s means, your video will have 30 frame per second with every frame or every picture takes 1/60s exposure of light.
Faster shutter = Crisp Picture but Darker due to short exposure of light (higher iso is needed to keep brightness level steady).
Slower shutter = Blurred Picture but brighter due to longer exposure (consider night traffic photo with long trails of car lights).
Rotating blade is one of a good example on showing how shutter speed in video works.
The lower shutter speed will give smoother movement, but the blades are actually blurred when the video is paused. On the other side, high shutter speed will give a stuttering effect and may not be pleasing to watch, but the frames are razor sharp when paused.
