You tie up a pony-tail on the front of your head, like a unicorn, then chop off hair in a straight line. Then you cut in to soften the lines.
I tried this on my long damaged hair. I made a few trims until I got the length I wanted. I love the layers it adds and now my hair looks healthy and styled.
Here's detailed instructions from Cosmo UK.
I also checked out this video.
I used these sheers from Sally's Beauty.
The process took me less than 5 minutes and I saved a bunch of money.