How is the doppler effect related to understanding the universe?
It gives us proof that the universe is expanding by showing us a red shift. It can also show us which way objects are revolving.
As objects moves away from use the light waves they emit become stretched out. The longer wavelengths of visible light are at the red end of the spectrum so the light is shifted toward the red end.
According to the Big Bang Theory, everything in the Universe is moving away from us, or we are moving away from our solar system. However because objects revolve around other objects, on occasion we get an object that shows blue-shift (the opposite of red-shift). This is because the object is at the part of it's revolution that it is moving toward the Earth, even though generally speaking it is still moving away from Earth.