I'm not sure exactly what you are asking, but I'll give it a shot.
As the others have said, read more <a href="http://0-2u.com?go=books" onmouseover="window.status = 'goto: books';return 1" onmouseout="window.status=''">books</a>, and take notes in the field so later you can see what you were doing when the pics turn out or not.
First of all, are you using the flash built into your camera? The little pop up flashes are no substitute for a full sized flash unit. They are too close the the axis of the lens; this increases red eye. They are not powerful enough for many situations. I only use the pop up flash for daylight fill and sometimes as fill in combination with an off camera flash (some dedicated flashes have a sync mode for using the pop up as fill).
A regular flash unit will be two or three times as powerful as the pop up. On camera it will be far enough away from the lens and eliminate red eye, and you can use it off camera to adjust the direction of the lighting. The flash unit will probably have several auto modes and a manual mode.
Flash power is refered to as the guide number (GN). GN may be in meters or feet. GN divided by distance to subject equals f/stop for ISO 100 film. So if your GN is 80, your subject is 10" away, and you are using ISO 100 film then your aperture would be f/8. Shutter speed should be set at flash sync speed or slower. This is just a general guideline though. You are going to have to experiment to see how you think it looks best. Do you like to underexpose the background by a stop? Or do you want the fill one stop less than the background?
A "dedicated" flash will be designed specifically for a certain brand or model of camera. Dedicated flashes usually perform pretty well with the camera on auto, and may have other special features (such as the pop up sync mentioned above). "Non-dedicated" flashes are designed to work with any camera.
As far as when to use it? I'm imagining the pics I see in my local paper and I'd say that I think I'd use the flash about 95% of the time. If there is a person in the pic within 20', I'd say use a flash, even outside in the bright sun.
When in doubt, and until you get a feel for this, take two of every shot, one with flash, one without. Then you'll see what the difference is in every situation.