I will try to explain it myself. The "Edge" is the edge of something magical, the orgasm. You gonna stay on that edge without ejaculating no matter what, for as long as you can/have time to do so. When you have sex you do it intentionally to be a good lover. In PE you do it intentionally to gain size. That edge is what is going to give you maximum expansion without any tools but just blood flow. You may notice that when right before orgasm and while orgasm that your penis is filled to maximum for a while and getting like a "pump". You gonna look for this feeling over and over again when you edge. Do keegels aswell. If you feel like you are going to orgasm, do a strong keegel to keep orgasm away and still reach that "Edging pump". Don't ever do a quick masturbate with ejaculation.
When you feel you gonna cum, stop for 3-7sec and keep going until you feel you are gonna cum again. People often tend to say that you should stop completly when you feel the urge to cum and then go again. I would say when you are edging for size and not in bed, try to be at the "urge" moment as much as possible. If you stop for too long the "urge" feeling will pass and you will not reach it as easy as before. You need to reach it as much as possible to keep the eding pump going.