Getting is is merely a matter of gently easing up on the throttle until your mpg readout goes to 100 mpg or even higher. Then you just feather the throttle around this point and still get some acceleration but stay in that miracle mpg range.
If you are slowing down too much on a hill or the road is too bumpy, you may have to give it too much gas and then drop out of lean-burn. If you back off too much, then you may start to see regen breaking - and likely you are in fuel-cut (no fuel at all - and no acceleration at all possible except via gravity).
How it works is best explained by someone who knows the technical details of the Honda magic.
If you are test driving one, try getting the car up to abour 30 mph or so on a flat road section and then while you are in 4th (or even 5th) ease up on the gas while watching the instantaneous mpg readout. You should see it go to about 100 mpg and stay there or higher. You will find that you can still give it some gas and accelerate even at 100 mpg.
Have your co-pilot make sure you don't wreck up while you are staring at the panel meters!
Once you get the hang of it, you can look less.
The purge is where you are in a happy lean-burn state and suddenly your mpg goes down to about 50. It is Honda burning more gas to make the cat hotter and clean it out. You can back way off on the gas, and get it back in lean burn. I never figured out why you can kind of abort the purge in this way. If you can just abort it, why do it at all? Hmmm.. That is something to worry about after you get the hang of lean burn. It is kind of a refinement of lean-burn to avoid the purge.