The Doppler effect is actually really simple. Think about the waves on the ocean, and for simplicity's sake all of the waves are perfectly the same exactly like you know sound waves or something are. Since you are just floating and not moving, the waves hit you, say 1 every 10 seconds. If you swim towards the waves though, they hit you quicker, say 1 every 5 seconds. If you swim with the waves, they hit you less often (but they hit you from behind, you don't swim into them), at maybe 1 every 20 seconds.
That's sort of how the Doppler effect works.