What does metering do in M mode?

[HyperYagami]

As the exposure is controlled by the combination of shutter/ISO/aperture...how does metering fit in there?

THANKS!

[monochrome]

The metering simply gives you the information so that you can make adjustments to shutter/aperture/ISO instead of the camera.

[gofer]

The metering actually does nothing in 'M' (manual) mode except give an indication. The general idea is that you should balance the aperture, shutter speed and ISO appropriate to the shot being taken to bring the meter to the centre of the scale (but not necessarily of course if you decide otherwise)

(edit : bugger, must type faster)

[Zansho]

The metering functions as a "guide" of sorts, it'll tell you how your selection of F-stops, shutter speeds and ISO will expose the image. Depending on the metering choice (average, evaluative, spot metering) you can adjust your settings to your liking.

Generally speaking, a good exposure will be in the "middle" of the metering line bar. Keep in mind, that it should be used as a tool for you to decide if that's how you want to expose your image - do you want it to be slightly under exposed or overexposed for artistic purposes? Adjust your settings so that the indicator in your meter shows that particular adjustment that you made.

It's not foolproof. The meter in the camera is reflective, not incident, and you have to take that into account. It's an information tool for you, the photographer, to use and make informed judgments about how you want to expose your image.

P.S. read your manual. It has a nice section about your in-camera's light meter.

[Lotto]

The meter in M mode is the same as Av, Tv and P mode, except it does not change value once the user sets it.