Set up a still-life arrangement, with any object or group of objects. The lighting direction will depend on your subject, and you might like to experiment, but, if in doubt, fix the naked lamp more or less overhead, pointing down.
Using a diffused light source to soften the shadows and highlights take two photographs, one with just the naked lamp, the other with the translucent material held between the lamp and your subject (but out of view). The two exposure settings will be different.
Look at the results, and write down exactly what you see as the differences. Look at the strengths (blackness) of the shadows, their extent, and the hardness of their edges. Look also at the highlights, and at the contrast. Finally was the diffusion an improvement? Record your answer.
I used my Nikon SB 700 speedlight for this exercise and a couple of Yongnuo RF-603N II wireless flash triggers that I bought recently and had not yet put to work. The still life was set up in a light tent, with a black background and a hessian sack roughly arranged on the floor of the tent on which I placed a large log and perched the wooden rooster on top of that.
In fig 1, the photo taken with the bare flash positioned at about 45 degree angle from the rooster. The flash head was pointed one click up from the straight on setting so the light skimmed over the top of the rooster’s head. There is a noticeable shadow behind the rooster’s tail. There is also a hotspot on the rooster’s neck from the flash.
I had actually forgotten to change my exposure when I made the second photograph, but I know that adding a diffuser into the mix can decrease the light by up to 2 stops, so I adjusted the exposure in post processing until the saturation and intensity of the red of the rooster’s head in fig 2 matched that of fig 1. It was only one stop difference, so had I exposed correctly, my aperture would have been f5. The diffuser got rid of the shadow and the black background is evenly lit and more saturated. The hotspot on the rooster’s neck is still there, but it is a fraction smaller and less bright. This is probably where a small gobo should be positioned between the diffuser and the subject to eliminate that hotspot. Unfortunately I did not have enough hands to do that piece. The diffuser causes the flash to cast a more even light as can be seen by the exposure on the hessian sack. It is a little brighter in fig 2 and the shadows in the folds have also lost their harsh edges. Fig 2 is definitely more pleasing to the eye.
The lighting diagram for the setup can be seen below.