For the most part, it simply doesn't. The camera sets an exposure. At least in the simple case, it takes whatever amount of light is coming into the meter, and sets the exposure to make that into a fixed level somewhere in the vicinity of 18% grey. The more complex case is the multi-spot metering (goes by several names, but makes little real difference). Based on its measurements, it might decide to adjust the target exposure level to (say) 12% or 27% or whatever, but that's about it -- it's still only 1) measuring the light and picking some combination of shutter speed, aperture and (possibly) effective ISO to achieve the exposure it's picked.

While most digital cameras do some post-processing, it's not (at least normally) adjusted based on the content of an individual picture -- it simply has a tone curve for a particular setting, and adjusts tones based on the curve you've selected (high contrast, portrait, scenic, etc.)

Depending on the input you capture and the curve you select, that might be about the right contrast range, or it might be too little or too much. In theory, it could do quite a bit more, analyzing the histogram to decide on adjustments in roughly the same way as something like ACR does for its "Auto" exposure adjustment -- but at least in most digital cameras you don't get anything very similar to that.