I was introduced to heat embossing a few years ago at a Stampin' Up workshop. At first I was really nervous and not sure what I was doing, but after a few tries I realized what a cool technique it was!
Supplies you will need are your stamp of choice (both rubber stamps and acrylic stamps are fine for this), versamark, a versamarker or versaink, embossing powder, a small paintbrush, a heating tool, and I like to have a funnel tray (although a paper towel or waxed paper will do nicely too).
First you want to ink up your stamp with your versamark, make sure you thoroughly cover your stamp but don't flood it or your detail will be ruined. Then ink your paper, if you are using versamark it will leave a watermark. Shake your embossing powder entirely over the stamped image, it should be entirely covered. Hold your image over your tray or waxed paper and tap off all excess powder and return to jar. With your small paintbrush sweep off any extra powder as this will melt when heated and show in your finished product.
Once you are happy with your powdered image get your heating tool out and turn it on for a few seconds to let it heat up. Hold it directly over your image but not to close, you can singe the paper. You're image is embossed when it turns from powdery to glossy (if you are using a distress powder it will not gloss). It usually takes only 2-3 seconds for it to change. Make sure you get the entire image glossy and then let it cool off. It will be a beautiful raised image when you are done.