For this exercise you need a lightbox or at least a light source that is behind the subject. A lightbox can be very useful to photograph translucent subjects like leaves but you can also photograph other subjects and create some interesting images. Sp try your best to photograph subjects that are illuminated from behind.
I found some cough drops in my office and decided to photograph them. I had to overexpose by about plus three fstops to get this image.
Enjoy and keep on photographing!