Beginners guide to using on camera flash
So you probably have a new DSLR or new camera of some sort. You might have even upgraded your camera and still don't know flash compensation and what it does. Getting any new camera and learning all the buttons and menu is pretty stressful, not to mention what everything means. But for those who may not be ready to shoot Manual, Program, or even Aperture Priority.
Knowing you have an on camera flash is half the battle, but knowing how to use it is the greater half. Most importantly to manually adjust the exposure compensation and the strength of the flash must be done in a mode other than AUTO where you can properly adjust available light, aperture, and ISO that will fit the amount of light used.
Now there is no exact number or exact format to setting compensation, what I mean by this is, you will not get the same reading all the time. Someone else may have a different reading based off lens, censor size or even the actual age of the camera (seeing cameras get better over time). The amount of flash you put out of the camera can be adjusted so you get less shadows, below is a menu set up and also a quick menu set up when shooting manually.
Knowing how much to use in an image so an image isn't over exposed or blown out. This is one of those things that most people don't realize, a lot of the time fill flash is used outside and to compensate for a shaded area (in general fill flash is for that or to add a little highlight). What exposure should you use for fill flash? Well keep in mind how much available light you have, dim light in a corner, sunset, direct sunlight, sun rise? Think about how much light you don't have so far and what you might need to compensate or how to get just a little extra fill.
Optical Trigger Flash (commander mode, etc)
If you don't have a pocket wizard, you can always use the pop up flash to trigger other speedlights, strobes, etc. In this case, it doesn't mean you are actually using the pop up flash for actual light, but more to control other light sources. (Primarily studio lighting and Speedlights)