You literally shrink and stretch the material.
In the case of the sample about 15mm (3/5 of an inch) on a length of about 20cm (about 8 inch).
So 3/5 inch stretch in 8 inch, and 3/5 of an inch shrink in 8 inch.
When you look at it it seems pretty much.
Also when you measure the thickness of the material with a caliper you can see the changing of the thickness .
The stretch side got about 0.1mm thinner,
and the shrink side about 0.1 mm thicker.
Now remember to take it slow and work from the edge slowly inwords.
Very small pumps and not to heavy with the handle of the forming blocks at a time.
And working on your actual workpiece, keep your workpiece at least 1 inch longer per side. This keeps the teeth of the formingdies away from the edges, and your "bend" wil go till the end of your sheetmetal piece. As you can see on image nr.2864 on the left side of the bend.
The complete S shape took me about 20 minutes