How to set up and correctly use the light meter on a Nikon D3100?

I have a Nikon D3100 and I want to learn how to use the light meter to get the best out of my exposures? I tried looking online and could not find the information I needed. How to do use it and how to I access it on my Camera?

Do you mean the internal metering or a hand-held light meter?

The internal metering works with three types: Matrix (all around metering), center, and spot. Where ever your focus selection is, the camera will do its best to read the reflected light, and give an overall "good" exposure.

Besides the different patterns that the meters is able to read, understand that the meter can only do one thing. That is read middle gray. Middle gray is like you might suspect it is perfectly in in the middle between back and the bright white. The camera itself can't see color, even know it takes color pictures. The way the sensor is set up, photons of various colors are recognized, but they are only numbers. You might say that the camera sensed X amount of blue, red, and green, and that is a color picture, but the camera itself is color blind. It takes software to actually read the numbers and make the colors.

Anyway what that means is everything is black and white to the camera, so it see's everything in gray. The meter will tell you how gray something is. It might be dark gray or more white. What we do as photographers is break up the tones into 10 distinct categories, starting with pure black and ending with pure white. We call these categories zones. Here is a description on the zones.

Zone zero is pure back.
Zone 1 is just off pure black
zone 2 is black with texture but no detail
zone 3 has both texture and detail and is considered shadows
zone 4 is the tone of black peoples skin
zone 5 is middle gray
zone 6 is Caucasian skin
zone 7 is white with texture and detail
zone 8 is white with texture
zone 9 is pure white.

Now here is a neat part, every zone is exactly twice as bright as the previous one, or if your counting down they are half as bright. When something is twice or half as bright, we call that a full stop or stop for short.

To use you meter, you point the camera, and partially press down on the shutter to activate the meter. The meter will respond telling you if what you metering is brighter or darker compared to middle gray. To make that practical you simply adjust the camera settings so that what your shooting is exposed correctly. Lets do some examples.

You decide to shoot a picture of a light skinned friend. Your camera is set up for spot metering and so you point the little tiny box in the viewfinder at your friends face. The meter reads +1 that means the camera thinks that what it is metering, your friends face, is 1 stop brighter than middle gray. Since light skin is zone six your camera will make the right exposure, so you can go ahead and take the picture.

Now lets say your taking a picture of a house. The picture you want is in a shadowy area. Now if you point the little meter thing at the house shadowy area, the meter will say, that to make that area middle gray, it is going to overexpose the shot. Well you want a shadow, not an overexposed image, so you need to adjust the camera so it takes in less light than what meter wants you to do. So using the adjustments on the camera, you take away two stops of light. This is done by making the shutter twice as fast, twice, or by making the aperture smaller by two stops. After you have made these adjustments to your camera, you meter again. This time the meter will say what your pointing at is -2 on the meter. Since you know that your shooting zone 3 you know that is what you want so you can go ahead and take your picture.

The thing to remember is look at how bright something is and remember the different zones. Then set up your camera so that what your shooting matches those zones. In the end, you will realize that you can meter anything, just set your camera accordingly and you'll never take a bad shot. Remember also that cameras are pretty stupid, but your smart. It takes a little practice, but after a while you won't know any other way.