All humans would be exposed to cosmic radiation that falls from the atmosphere due to -100 degree temperatures. Without the sun there would be no photosynthesis, causing all plants, animals, and humans to die.
Sun or stars?
Every sun is a star, but not every star is a Sun. The Sun is larger and as such a lot brighter than most stars. There are billions of Suns in our galaxy alone and as mentioned, many of the stars we see are also Suns. But many celestial objects you see when looking up are not stars.