Diane,
Photography is made up of 2 different aspects. The first is the technical use of the tools of the trade, cameras, lenses, light, and exposure.
The second aspect is aesthetics. The previsulization of what we want the photograph to look like. We choose what we want to photograph and then what to include and exclude from the frame. We use graphic elements to express what we want the photograph to convey what we had in our mind.
This is how photographs are created. This is what makes the difference between a photograph and a snapshot.
It sounds like you have a good grasp of the aesthetics but not the technical.
When I asked you why you were a professional and asking such a basic question of exposure, I wan't inferring anything. I was asking a question to get more info, because I was confused. I don't infer anything, I come right out and say it. I didn't say that you were deceiving anybody.

Now that we know that you are basically a beginning photographer that is getting jobs and that you want to improve your skills, all of us here can probably guide you along with the knowledge that you need.

This would be my recommendations. Get any book from John Shaw or the book by Bryan Petersen, study them and try to understand what they are talking about. Use your camera with your lens along with the book. If after this, you still don't have a good enough grasp of exposure, then take a seminar course, photo safari or work with another photographer until you have the skills you need in exposure. Understanding apertures (F stops), shutter speeds, and light sensitivity (iso) can be a daunting experience, but crucial to your success.

What do you have trouble with? F stops? Shutter speeds? ISO? a combination of these or the interrelationship of how all 3 work together?

Shutter speeds and iso are the two easiest to understand for most people as each doubling or halving of light is also doubling or halving of the number (i.e 500 to 250, 500 to 1000, 200 to 400, 200 to 100).

F stops is the hardest for beginners to understand because each halving or doubling is based on alternating multiples of 1 or 1.4 (i.e 4 to 5.6 or 4 to 2.8). Each time I doubled or halved the amount of light but the number of the f stop did not double or halve.

In most lenses, your f stops will be 2.8, 4, 5.6, 8, 11, 16, 22, 32. Notice that every other number in the scale is a multiple of 1 or 1.4. The difference between 2.8 and 4 is 1/2 the amount of light. 2.8 allows more light into the camera than 22. You can see this for yourself by taking a lens, holding it up to the light and turn the aperture ring from 2.8 to 22 and you will see the aperture at 2.8 is huge in comparison to the aperture at 22. Each halving or doubling of light is called "a stop". The difference between going from f/2.8 to F/4 is called "closing down a stop". If you watch that aperture through the lens you will see the aperture does indeed close up a little as you go from F/2.8 to F/4. Now go from F/4 to F/2.8 and you will see the aperture go from smaller to larger and that is called "opening up a stop". Each "stop" is either doubling the amount of light or halving the amount of light, depending on the direction you are going with the lens.

After you learn, understand and memorize the F stops, then you are ready to learn how the different F stops effect your depth of field. You will need to know the relationship between F stop and shutter speed and how sensitivity (ISO) effects the exposure. I could explain it all here, but essentially, I would be writing a book and with my arm in a sling, while I have the time, I don't have the inclination.

My experience is I have been photographing all my life and I am 56 years old. When I was a child, I used my parents Kodak Brownie and Graflex Speed Graphic cameras. I have been professional for over 10 years. I photograph Dog Agility Trials, Lure Coursing, Flyball, High school Sports and Nature. 100% of my living is made from my photography and I am a member of NPS (Nikon Professional Services). I have had my photos published in newspapers, magazines, books, brochures, calendar and note cards. I tell you this, not to brag, but to let you know my experience and how I use that experience.