Paul,
Edging is when you stop yourself jsut as you get the feeling that you might be about to cum, let the urge die down and then go for it again. Do this a few times ("tease" yourself), for up to a couple of hours if you want to and have the time, and you'll find that you will shoot a huge load when you finally do cum.
Each time you masturbate or start having sex your body prepares enough ejaculate for an effective "performance". When you back off it stores the ejaculate for future use. By edging you keep building up your reserves to produce a powerful orgasm when you finally allow yourself to let go.