Shoot mode is a whole host of lessons. Here's some basics. The i mode lets the camera try to determine what kind of scene you are shooting (portrait, landscape, action, etc) and makes the settings based on what it guesses. Frankly, I've never used it, it's for people taking snapshots.
For AP work, I like to use Shutter Priority (S). This means you set the shutter speed and the camera sets the corresponding aperture for the correct exposure.
For example, on a normal full sunlight day, if you set the ISO at 200 and set the shutter at 1/200 the aperture should be about F16. On Shutter Priority, the shutter will stay at 1/200 and the camera will vary the aperture depending on changes in the lighting.
Changing the aperture a stop or two to adjust for lighting isn't a big deal but I'd prefer to leave the shutter at a fairly fast speed for AP work. That's why I use Shutter Priority.
One other thing I like to use sometimes for AP is bracket control. If you press the left side of the control wheel, you should see a number of options on the right side of the LCD. This includes single shooting, continuous shooting etc. Scroll until you see BRK C and it's says Bracket Shooting. What happens now is when you press the shutter once, the camera takes three shots with three different exposures. That gives you three shots to choose from. Very handy when shooting AP and you can't immediately review your shot.
Good luck.
