To do this technique, you need a stamping platform, such as the Tonic/Tim Holtz Stamp Platform.
You need one "template" made from the negative that would normally be thrown away. The template can be reused. Cut as many of the actual shapes for stamping on as you want.
For example, I could do this with the matching die for the Lush Lilacs parasol stamp, that I used to make my Lush Lilacs card in the post shown just below this one. If I cut it in white, I might keep both the parasol shape, and the part that is left, the outline. The parasol piece will be set aside for stamping on later. The outline piece becomes the template. Or I might cut the template in a dark, heavier cardstock. In this case, I would keep the outline, but might throw the dark colored parasol away if I did not want to use it. A heavier cardstock is sturdier for your template and can be reused more times.
The purple cardstock was too flimsy for my template, so I ended up making my template from a sturdier black cardstock. I cut a few blanks from white, light purple, and medium purple cardstock. The medium purple was textured, which was a bad idea. I had forgotten that textured does not stamp as well.
I would also cut several additional parasol die cuts in white and lighter colors, but would throw away the outline/waste papers as usual. The die cut shapes are the "blanks" and will be used for stamping on as desired.
Put a piece of plain paper on your stamp platform and fasten it with magnets. Put your template on the platform base as well, then position the stamp so that it will be approximately in the center of the template. It does not need to be perfect. You just want to make sure you can fit the template. The first time I did the "cut first, stamp second" technique, I put the stamp on the platform lid without making sure I had left sufficient room on the base plate for the template. I had positioned my stamp too close to the edge and had to trim a corner off my template, which was annoying.
Once it is positioned, bring down the lid so that it picks up your cling stamp. Remove the template and set it aside. Ink your stamp, then stamp on the plain paper. Open the lid.
With the stamped, plain paper still in place, lay the template over the stamped image, so that it is outlined perfectly. Tape it to your plain paper with Washi tape, or use additional magnets if you prefer.
Now put your matching cut out into the template so that it fits like a puzzle piece. The template should hold it perfectly in position.