Youth PhotoExpo Zambia
In order to know when you have the right amount of light on your sensor, the camera measures the incoming light with a light meter. The light meter in your camera (if you have a SLR-camera) probably looks something like this:
Measuring light
Right in the middle is what the camera sees is the right amount of light, so try to aim for that. More to the minus-sign means you are under-exposing (too dark), more to the plus-sign means you are over-exposing (too light). You can control this by adjusting the shutter speed and/or aperture (assuming that you have already chosen your ISO). Every step to the left or right is called a “stop”.
But...remember you are the artist not the camera, so if you like it differently: do so!! There have been quite a few artists that have become famous for over- or underexposing their pictures. As long as you do it on purpose and not because you don't know how it works;)
Go for it!