Run- Making the piece you are painting so wet that the paint starts sagging, or a drip forms a line and runs downward. A vertical paint line that is thicker than the rest of the paint job.
Light application= Rough to touch, not pretty, looks kinda like an orange peel. Texture
Medium= Smooth application, wet enough to "lay out" and make a perfectly smooth surfact(bugs and dust aside)
Heavy= Like medium, but with a few sags and paint lines running downward on vertical panels.
Real Heavy= Waste of paint. Runs everywhere.
You want to do the least work possible to get a nice looking paint job. I shoot for medium. It takes a while to aquire the eye for spraying, but you'll get it. If I could not get the paint perfect, I'm aim for the heavy side slightly. It's much easier to rub out a couple runs than to wetsand your ass off on a light paintjob.
To conserve paint, and slow down how much paint you apply at one time:
Your gun should have a twist valve to control air flow. Crank that baby wide open unless you know what you are doing. This is seperate from your regulator and tank pressure. Just the gun.
It should also have a fluid flow adjustment. Close this valve completely. When you pull the trigger, no paint will come out. OK, now you open that valve about 1 turn(360 degrees). Grab a test panel. Turn that adjuster a little at a time until you can apply enough paint to finish a panel before it dries, and not totally saturate your piece if you move too slow. I have mine set so that my hand only moves the gun 8-12 inches per second. Overlap your passes by about half the width of the path.
That's a starting point. I am very sure that my way may not be the fastest, or the best, but it sounds like you need to crawl before you walk.
Fun isn't it? Don't be intimidated. Practice makes perfect.