It is an often stated widely repeated but just as widely misunderstood that using a camera in auto lets the camera make creative decisions. It doesn't. It merely follows your instructions - based on camera settings, camera profile, and picture controls. You are always in control, and choosing auto everything is a creative choice.

Part of using manual adjustments for all of the camera settings requires a solid knowledge of what the camera does for each setting.

Lets take a look at metering mode - most cameras have the following settings - average, center weighted, evaluative/matrix, and spot. Understanding which one to use and when to use it is where many people get stuck. So, as an example you are taking a picture of three dogs - a brilliantly white Samoyede, Black Poodle, and a a Grey Pit Bull - and these are all in the same light. One approach would be to set the meter to spot mode, which will measure a small part of the image - usually the center 1% to 15% of the entire frame. If you measure the grey dog, yo'll get one reading, if you measure the white dog it will reflect more light and you will get a different reading, and if you read the black dog, which will reflect less light you'll get yet another reading. Which one is correct? Well, all of them. You can probably use the reading off the grey dog, and both the white and black dogs will be properly exposed. But if you use the reading from the white dog, the white dog will turn out grey, the grey dog will be black, and the black dog will be without much detail. Camera meters are set up to produce a correct exposure for middle grey. The camera doesn't know what the tonal value is of your subject, so no matter what you are reading the result will produce a nice middle grey.

Your experience as a photographer will suggest that if you read the white dog, you'll need to make it brighter than grey, which you will do by raising the ISO, using a longer shutter speed, or using a larger aperture in the lens - or a combination of all three. In it's most basic form, this is manual exposure.
This explains how meters work.

http://www.digital-photo-secrets.com/tip/2879/which-is-best-spot-center-weight-or-matrix-metering/

Many photographers who shoot digital will also record their images as raw files, which allow for more control over the results - since nearly everything that you can set up in the camera you can set up in a raw editor - but the best part is you can have a custom set of adjustments that are specific to each image. Many shooters that do not opt for raw will "set it and forget it" and often not make subject specific adjustments.