The thing to understand about your camera's meter is it is a reflective meter. It measure the light reflecting off of your subject. So if you were to take shot of a flat black subject, it's not going to reflect much light, and the camera will try to over compensate and make your black subject gray. The opposite is true of a white, or shiny subject, it's going to under expose because your subject is very efficient at reflecting light.
So how do you get especially light or dark subjects to turn out properly in your exposures? Well there are two very effective methods, one is to shoot in manual and take a reflective reading - i.e. a test shot - of something that actually
is the exact color that the camera expects to see, like an 18% gray card, then use that same setting to photograph your subject. The other was use to use an incident light meter which tells you exactly how much light is falling on your subject, rather than how much is being reflected. The two methods, properly executed, should yield the exact same results. And a 5 dollar gray card is a lot cheaper than a light meter, you can also use it as a white balance target, or a lens shade
What a light meter is good for is setting up lighting ratios, or mixing flash with ambient light (which is also a ratio when you think about it). It provides speed, accuracy, reproducibility, and reduced post production time. I rely on my light meter at every shoot and I am never disappointed. Of greater importance than a light meter I would put a good lens, a tripod, and maybe a flash, (obviously you have a camera or you wouldn't be asking), but once you have all of those things, I would seriously consider a light meter as my next purchase. In the mean time though a gray card is a very good substitute.