The Questions about Camera Modes..

The mode dial on a modern camera usually includes a bewildering number of letters and icons. I can never remember what 90% of those modes do, and even if I did, I don’t remember to set that mode when the opportunity presents itself. But you can get by using just 3 of the modes, even 2 if you are desperate. Here are some clues to know when to use which mode.

"Set Sail With Me" captured by Thomas Hawk (Click Image to See More From Thomas Hawk)

The Program mode. This is the mode that I shoot in most of the time. The camera does the exposure and the focus. You can however set the exposure compensation, which is the only control (other than the flash) you need most of the time for snapshots. The nice thing about this mode is, it is completely automatic, but you have control over the flash, which is what you need for your snapshots.
The Automatic mode. This is what most people set when they look at a camera for the first time. The problem with this mode is that the camera will invariably choose the wrong moment to turn on the flash, usually ruining your planned picture. Really, just use mode P, and turn on the flash when you want it.
The Shutter Priority mode. Here, you can set a shutter speed and the camera will set the correct aperture for the light conditions. If you need to capture a speedy subject, choose a high shutter speed. If you want to blur the motion, choose a lower shutter speed. You can also play around with longer shutter speeds like 1-5 seconds to get nice some effects on water fountains or similar things.
The Aperture Priority mode. Here, you set the aperture and the camera chooses the correct shutter speed. It is useful for mainly two things. First is the ability to choose the depth of field, set a wide aperture for shallow depth of field and a narrow aperture for larger depth of field. Secondly, the image quality with almost all lenses are better when “stopped down”, i.e. not at maximum aperture, but a couple of stops below.

"Bokeh" captured by fady (Click Image to See More From fady)

The Manual mode. Here, you set both the shutter speed and the aperture. The camera does not adjust for the correct exposure in this mode. If you set unsuitable values and the exposure is all wrong, tough luck. This mode is useful in order to keep the exposure constant, when taking a couple of images to stitch together a panorama or something. I almost never use it.

The rest?

Well, there are many other modes, but like I said at the beginning, I could never learn them. But here is how you can cheat, and use one of the modes I mentioned above:
Portrait mode. Here, you want to have the background blurred and out of focus so that the whole picture is focused on your subject. You need shallow depth of field, so you need to use mode A, and set the maximum aperture (lowest f-number).
Landscape mode. Here, you want to have pretty much the whole picture in focus, everything. So, you need a wide depth of field, simply set mode A, and choose a lower aperture (low f-number). It is a good idea not to go with the lowest one, because diffraction decreases image quality, go with 1/3 from the bottom (f11-f16?).

"St. Andrews' Pier" captured by Ryck Valli (Click Image to See More From Ryck Valli)

Sports mode. Here, we want to freeze the subject motion. In order to do that, we need a high shutter speed, set mode S and try to guess a suitable shutter speed. Take a few test shots to see if your chosen shutter speed can “freeze” the motion. If not, choose a higher one. On the other hand, if you want to blur motion, you should choose lower shutter speeds.