Yes, the nubra sticks to your clean, smooth chest and you pull the two sides toward the middle (I stick mine several inches apart to get good boobage), then fasten.
When you're done, just peel off the nubra, clean with mild soap, and air dry.
If you're utterly flat, they're a no-go. If you have some extra weight, or have even a small amount of chest muscle, they'll work, at least somewhat. In lieu of eating lots of doughnuts, try doing pushups to build up your pectoral muscles.