Don't get hung up thinking about snow and sand--those were only examples. Think about it this way:
Your camera meter is giving you the proper exposure based on the metered area being approximately the same light value as middle gray. If you are shooting general landscapes, flowers, houses, or even light-skinned people, this value is fairly accurate, but in other cases it is not.
If you point it at a white lilly, the camera says "OK, you want the lilly to be middle gray". If you point it at a black dog, the meter says "OK, you want the dog to be gray". In these cases, you have to compensate for the meter's thinking. Light measurements are all about shades of gray and not about color.
If you want to know what middle gray looks like, go into photoshop and fill a new document with a color that is R=192 G=192 B=192. That is middle gray.
Now take some of your photos and convert them to grayscale images and you should be able to see how the camera views light values. Look for areas of the photo that are like the 192-192-192 document you made and you should see that they are in the general center of the exposure.
This is one of the most important concepts in photography. I suggest you do some experiments to see exactly how it works. Take some bracketed shots of white and black objects to see how the camera handles them. In reality, bracketing is just a lazy method of exposure compensation.