You have a single lens reflex camera but don't really know much about how it works. Here is a lesson plan to get you on your way to understanding how f-stops work.
This exercise is a variation on an assignment from a 200 level college photography course. Having taught college level art courses for over ten years, I have created processes that teach through doing rather than through watching or listening. Following the process outlined below, you should be successful at having an educational experience to build upon.
Choose a scene to photography. You are going to photography this same composition many times. You may want to set up a tri-pod. Your composition needs to have a foreground, middle ground and background. In other words, have depth to your composition. A nice landscape with some interest on a sunny day would work well.
You are going to take the same photograph using every f-stop you have on your camera's lens. Have your roll of film printed for a visual comparison. If using a digital camera, prints would work best for this exercise. Mark on the back of each photo what the f-stop was that you used. The easiest way to do this is to keep your photos in order until you have made notes on them. Keeping a working journal of the kind of film, the light that is available and your exposure helps to be able to refer back to it, should you ever need to duplicate a situation. You may even want to create a small photo book of this exercise to refer back to it. In this case, your notes would be a nice addition to this book.
What you should see and why
As the f-stop numbers get larger, the reverse is happening to the lens opening. So f-16 would have a smaller lens opening than f-8. The smaller the lens opening the less light that is being let into the camera's lens but also the more composition that is in focus, or depth of field that is in focus. Try this, poke a pin hole into a piece of paper and hold it up to your eye, try to look through it holding the paper at different distances to your eye, this is similar to what is happening in the camera's lens with the f-stop. Another way to remember this, large number equals small lens opening, small number means large lens opening. In your prints, you should see different elements in your composition being focused upon and then becoming blurred. If this in not happening, you are not doing this exercise correctly.
Depth of field: as the range of distance from the nearest to the farthest subject from the camera that will appear acceptably sharp in a print. The depth of field is limited by the focal length of the lens, the aperture used and the distance at which the lens is focused.
ASA, ISO, exposure, focus, shutter, aperture, depth of field, focal length