I'm a beginner, and I have a Nikon D5100. Many times I come across the suggestion to "Check the meter reading for exposure."
Where can I find this reading and how do I read it?
I haven't used that actual camera but usually the meter readout is shown through the view finder. On cameras I have used its shown as a graduated scale at the bottom of the viewfinder with a pointer showing how far the current exposure is away from where the camera thinks the exposure should be. The scale will be 0 at the centre +1 (overexposed) on the right and -1 (underexposed) on the left. The idea is to get the pointer as close to 0 (ideal exposure) as possible.
Note this is where the built in light meter thinks the exposure should be, its not always correct especially in challenging lighting conditions but its good enough most of the time.
Cameras operate in a number of exposure modes:
In all modes except Manual (M) and Bulb (B), the camera meters and sets the exposure based on its metering mode. Because the exposure is set on your behalf there is no reading, although you can apply Exposure-Compensation to makes things brighter or darker.
In Manual mode, you are in control of exposure, so all DSLRs show you a scale which compares the exposure you set with the camera's metered value. This is the meter reading you are looking for. In your camera it will appear in the viewfinder below the frame as a scale going from -3 to +3. When the indicator is exactly in the middle (at zero), the exposure you set matches exactly the camera's metered value.
NOTE: For the camera to show the meter it has to have actually metered the scene. This normally happens on the half-press of the shutter which activates the meter. Before pressing the shutter half-way and after a certain delay (10-30s, depending on camera and settings), the meter reading is not shown. When you are not in M or B modes, the scale is used to show EC instead.
when you look through the view finder, you will see a calibration at the bottom. the bar indicates the exposure value, if the slider is to the left its under-exposed, to the right means over exposed.
Thats one way to find out about exposure using the camera, although the meter reading that you are talking about is slightly different, afaik. There is a separate device that measures the luminescence and is used by professional photographers.
Have you tried pressing the "i" button to change between "live view" and the control panel. The meter reading is a combination of the ISO (Sensitivity/Sensor Gain ) F Stop (How much light the lens will let through) and Shutter Speed ( What it says on the tin )
Not sure on that camera but in manual mode there may be some sort of gauge to advise you how much under/over exposure the current settings will give.
When you look through the view finder you will find a marking scale at the bottom. Thats the exposure meter. If you do not see it, press your shutter button half way down and it will be visible. Theres a needle that points on the scale. As you change the exposure, the needle will move to either the (+) side or (-) side. Try getting it to the center (0) for getting proper exposure.
But this meter calculates the amount of reflected light and may not always be accurate.