Aperture Priority Mode (A or AV)
In Aperture Priority Mode, you have control over setting the aperture (or f-stop). This means that you can control both the amount of light that comes through the lens and the depth of field. This mode is particularly useful if you’re concerned about having control over the amount of the image that is in focus (i.e. depth of field), and are photographing a stationary image that won’t be affected by shutter speed.
Shutter Priority Mode (S or TV)
When trying to freeze fast moving objects, shutter priority mode is your friend! It’s also ideal for times when you want to use long exposures. You’ll have control over the shutter speed, and the camera will set the appropriate aperture and ISO setting for you. Shutter Priority Mode is especially useful with sport and wildlife photography.
Manual Mode (M)
This is the mode that pro photographers use most of the time, as it allows complete control over all the camera’s functions. Manual mode means that you can adjust all functions to suit lighting conditions and other factors. However, using manual mode requires a good understanding of the relationships between different functions — in particular of the relationship between shutter speed and aperture.