(If you haven't read the Introduction to Radiology Fun yet, now is a good time. We'll wait for you.)
A picture is worth a thousand words. Here are two pictures of radiographs of a cat's abdomen. You can see all kinds of cool things here. The second picture is labeled so you can compare the two and find different organs.
This cat is lying in the standard position, flat on his right side. His head is to the left of the picture, and you can see his little tail vertebrae coming from the pelvis out the picture to the right.
This fat cat (left) has pretty visible kidneys, as well as the classic granular-looking stuff in the colon, which is fecal material (poop). The dog on the right is a good example of intestinal gas. Remember, air (gas) on a radiograph is dark/black.