This is a had topic to grasp but understanding how your light meter works is fundamental to getting exposures.
It’s important to know that your camera’s light metre is calibrated to whats known as middle grey. In short your camera wants to turn everything you point it at, to a middle grey.
Now for a lot of scenes this is generally ok, but as you get better and more familiar with your camera, you will also want to make artistic decisions for your self. So instead of the camera telling you what you want, you have to know what adjustments are necessary to achieve your vision of what the image should be.
If you point your camera at a white wall you would reasonably expect to get a white image on your LCD. But thats not the case. Your camera wants to take that white wall and make it middle grey. so to realise your vision you need to make adjustments that tell the camera to make the image white.
The target above is a calibrated to middle grey and very useful as a reference.
If we look at a chart showing tones going from black to white, we can see that white with detail is +2 stops from middle grey. Conversely if we look at -2 stops we have black but wuth some detail.
We can use this information to help us get the correct exposure for a given scene.
Say we are going to take a photo of a white swan, then its important that we retain detail on the bird. We know the bird is not pure white, so we can asume +2 stops will give us white with detail. With me so far?
Next we zoom in and fill the view finder with the bird and dial in the correct exposure +2 stops.
Now take a test shot. If the image is to light adjust, to dark adjust.
Next up The Histogram, your best friend…