A darkroom is a special place where people make photographs before computers could do it. It's called a darkroom because it needs to be very dark so that the light doesn't ruin the film (the thing that captures the image).
So, how does it work? First, you take a picture using a camera and then you take the film out of the camera and put it in a special machine called a film processor. The film processor puts chemicals on the film to bring out the image.
Next, you take the film out of the processor and hang it up on a special wall inside the darkroom. Then, you turn on a special light called the "safelight." This light is a special color (usually red) that won't ruin the film.
Now, you have to make a print of the image on a special paper called photographic paper. To do this, you take a negative (the opposite of the photo on the film) and put it in a special machine called an enlarger. The enlarger shines a light through the negative and onto the photographic paper.
After a few minutes, you take the photographic paper and put it in a tray of chemicals. The chemicals react with the paper and bring out the image. Then, you put the paper in another tray of chemicals to stop the reaction. Finally, you rinse the paper in water to get rid of the chemicals.
And that's it! You now have a beautiful photograph that you made all by yourself in the darkroom!