Metering for Part of Any Scene
Partial Metering (Pink Area Below) - This setting is useful when your subject is strongly or overly backlit. The metering is weighted towards the centre of the viewfinder covering approximately 13.5% of the area. This will inevitably lead to your subject being correctly exposed, with a blown out background.
This effect can be quite nice and concentrates the eye on your well exposed subject. However, if you wanted a more evenly spread image it is worth having an image that is "slightly" overexposed behind the subject with the actual subject being "slightly" underexposed. You can then darken the background and lighten the subject later on for a more evenly spread exposure.
Try playing with partial metering the next time that you are out and about in the sun. Place your subject with the sun behind and aim the central part of the viewfinder on them. Test it in various positions and see how the exposure fluctuates whether using aperture or shutter priority.