It is made by placing a sheet of photographic paper under the enlarger, arranging objects upon it (paperclips, jewelry, ferns, etc.), and exposing it to the light of the enlarger for about ten seconds.
There should not be a negative in the enlarger.
Make sure the light from the enlarger will cover the paper area before starting. (Do not expose the paper yet.)
You can also cut out dark paper and make outlines. Place the outlines on the photographic paper and then place other objects on top of the opening. Experiment for different results. The two pictures are examples of this type of photogram.
The result should be a white silhouette of the objects you placed on the paper.
Click on either picture to see a larger image.