Finally, what do these fluctuations mean?

The CMB is slightly anisotropic. Rather than be uniform everywhere, the CMB is anisotropic by one part in a 1,000. Studies of these variations in the temperature (and therefore density) of the CMB show the distribution of matter and energy in the Universe.

 

Why is this important? The temperature fluctuations also mark fluctuations in density fluctuations and it is from these fluctuations in density that all cosmic structures that exist today were formed! Images of the cosmic microwave background allow us to “see” areas of greater and lesser density, thereby linking observations of the present day distribution of galaxies to the Big Bang’s model of the Universe’s creation.

Sources:

http://lambda.gsfc.nasa.gov/product/cobe/

http://www.astro.ubc.ca/people/scott/cmb_intro.html