In a dSLR in M mode, your main guide to exposure is the light meter in your viewfinder. Because your viewfinder shows you the light in the scene, not the exposure on the sensor.

In all the automated exposure modes, the camera works hard to automatically adjust your settings to push the "needle" to "0" (where the auto-exposure systems thinks you'll get good exposure); so you may be thinking of that as your exposure compensation scale rather than a light meter. But in M mode, that needle can be anywhere on the scale, depending on how you've set your iso, aperture, and shutter speed. And that meter is telling you where the camera thinks the exposure is sitting.

If your frames are all coming out black, you're underexposing a lot, probably by -5EV, and the needle will probably be pegged all the way to the negative end of the scale (since on a D7000 it only goes to -3EV). That scale is marked out in stops (EV), btw. And you need to keep adjusting your settings until the needle heads closer to "0".

Sidenote: "0" may be close but not exactly right because metering can bias if a scene is mostly light or mostly dark, which is why we like to use M to override it, since we know what type of scene or look we're going for while all the camera can do is measure light in a scene. But if you use M mode and just set the needle to "0" all the time, you might as well use A or S modes instead: they'll do it faster. :)

In the case of underexposure, you need to adjust any of your three exposure settings to get more light: a slower shutter speed, a bigger aperture setting (smaller f-number) or higher ISO.

As I wrote above, the meter is marked off in EV, which can guide you in how much you need to adjust a setting. 1EV is a doubling/halving of the light. So with ISO and shutter speed that's doubling/halving the value. IOW, if you were -5EV and you wanted to only adjust that with ISO, you'd have to double your ISO five times (e.g., 200 to 6400) to get that. If you were doing it with shutter speed, you've have to double your shutter speed five times (e.g., 1/2000 to 1/60s). And with aperture, you'd have to go five stops on the f-number scale (e.g., f/16 to f/2.8).

Another alternative to using the meter, however, would be put to the camera into liveview and use exposure simulation so that you can see how the exposure changes as you change the exposure settings. But on a DSLR, you can only see this simulation on the back LCD of the camera, not in the viewfinder as you could with a mirrorless body.