Knowing how your camera sees the tones in a scene will help you get the exposure you need
There are three main metering patterns in DSLRs - pattern, center-weighted (a throwback to old manual cameras) and spot or partial, for pin-point accuracy.
Let's face it, most of us stick with the pattern metering system in DSLR cameras. In most circumstances it can be relied on to come to the right calculation, but you need to be aware of the conditions when it might be slightly off - and how you can put things right for your DSLR cameras. To ensure you never miss the decisive moment, you will need to know which way to turn the control dial to get the effect you want without having to take your eye away from the viewfinder. If you are shooting action for instance and you want to alter the settings quickly in order to go from frozen motion to creative blur, you need to know which direction gives you a smaller aperture/slower shutter speed of your DSLR camera. The same goes for dialling in exposure compensation - which direction reduces exposure and which increases it?
Center-weighted metering of DSLR cameras can be relied on when you are shooting protraits, as it biases its reading towards the center of the picture, where your subject is likely to be. Its results are more predictable than pattern metering, as you don't have to second-guess the complex algorithms the DSLR camera uses for pattern metering.
Spot-metering of DSLR cameras is the perfect accompaniment to Manual mode, although "Semi-manual" is often one of the quickest routes to good exposures. By combining Aperture Priority (or Shutter Priority) with spot/partial metering and the exposure lock feature of DSLR camera, you can get an effective on-the-fly "manual" mode. Point the DSLR camera at a mid-tone such as a pavement or grass in the same light as your subject, press the exposure lock button and recompose.