Quickly in this pill pointing you to the three cornerstones of featuring of light.
The first feature is very easy to understand, in fact it is the direction of the light on the subject. Is important to define the direction of light on the subject to determine the three-dimensional and fall of the shadows. Often refers to the light that Rembrandt is the technique he used the famous painter. This type of light is 45 ° from the subject and from above, as well as the painter used his lantern to portray his subjects. This type of light is in fact widely used in portrait photography.
Obviously with the direction of the light must be taken into account as this is compared to the focal plane of our camera.
With the quality of the light indicates the size of the light source. This fact determines the hardness of the shadows or their softness.
For physical nature a light small compared to the subject (as for example the sun) produces sharp shadows and incisive. A great light (for example a flash with a softbox very large or even a light windows) will produce very soft and soft shadows.
Finally we have the temperature of the light affecting the color of the same. A very low temperature (around 3200 ° K) denotes a very light amber and warm colors. A light at high temperature (about 5200 ° K) will be very cold and veers towards the blue to white (as for example the flash).
I have explained these are the 3 key features to understand the light, getting to grips with these features you will be able to handle light with aplomb.