Turning on the flash in "full auto" mode on my Nikon D50?

Simple situation that I cannot seem to figure out. When I take pictures in the daytime of a subject against a bright background, the flash does not want to fire on full auto mode. this results in a dark face, and a nicely exposed background. I want to make sure the fill in flash fires so that I can see my subject.

How do I do this?

Try this: with camera set in Auto, hold down the button on the left side of the flash, which I think has a lightning bolt on it. On the right is a little dial, roll it towards the top of the camera. The LCD screen should change the flash display and show you "Auto." After that, if the backlighting is strong enough, the camera is supposed to fire flash automatically to create fill. If it doesn't work, it may mean the camera doesn't think it needs the fill, in which case you should try shooting in P instead of Auto, where you should be able to control flash manually while the camera still operates the settings for you.

Well that's because of a situation called backlight. This is where the bright background is streaming into the camera's processor and telling it it's plenty bright. The result is no flash in auto mode. The camera then stops down the lens and you end up with bright backgrounds and darkened faces.

Ideally, you want to shoot with the main light source coming over your shoulder and lighting your subject. Not coming from behind them and into the camera. But if you can't help that, just use the manual flash setting. Turn on the flash and use it as a fill flash. Then it'll lighten your subject in spite of the backlight. You can also play with any scene/preset options which can help as well as any exposure compensation settings.