Most digital cameras these days – certainly Canons and Nikons – give you the option of shooting 4 or 5 different 'modes'. "P", "S", "A" & "M" and "Auto" mode (which doesn't, in fact, exist on my Nikon D300 but will be there on most DSLRs and every Digital compact). A quick rundown on what the different modes are designed for and then I'll give you my view which is nothing more (but nothing less) than that!
P stands for Program and allows your camera to select the basic exposure settings, but you can still override the camera's choices to fine-tune your image while maintaining metered exposure. S or Shutter priority is useful when you want to use a particular shutter speed to stop action or produce creative blur effects. Choose your preferred shutter speed and the camera will then automatically select the appropriate f/stop for you. A or Aperture priority lets you choose when you want to use a particular lens opening, especially to control sharpness or how much of your image is in focus. Specify the f/stop you want and the camera will select the appropriate shutter speed for you. M or Manual mode gives you full control over the shutter speed and lens opening, either for creative effects or because you are using a studio flash or other flash unit with your camera's automatic flash metering.
For some reason best known to myself I spent most of my first two years as a photographer shooting in S mode. I suppose I felt most comfortable with and I'm not a camera techie by any means! An encounter 6 months ago with my friend Paul Pacey in his studio revealed that he shot in Manual mode almost all the time. I was convinced by Paul's explanation as to why and started doing the same. Essentially it boils down to control. In Manual mode you control everything so as long as you have the time to fiddle around with the controls then there's no other way to go really; you fix the aperture setting and then you fix the shutter speed. The only occasions in which you might want to consider going into a different mode are if you are shooting high-pressured photojournalism – riots, car bombings, earthquakes that type of thing – and you simply don't have time to fiddle with the settings. On those occasions you might either shoot in Auto or P mode. Otherwise, working with moving subjects you might naturally move into S mode. This link has a good explanation of that. When you are looking for a strong Depth of Field (DOF) then Aperture mode might be for you but why not achieve precisely the same results – or better – in M?
It seems complicated but its really not. For 90% of your subjects – people, landscapes, buildings etc – 90% of the time you won't need to look beyond Manual mode.
