ok myloplex, I assumed that you knew at least what "exposure" means, and you were just asking a silly question. It seems that you don't know what exposure is all about. I shall try to be as comprehensive as possible:
You know that exposure by the camera is determined by aperture, shutter speed, and ISO right? Ok, the camera also has this nice gadget called a light meter which will analyse the scene and tell you what it thinks is the right exposure (i.e. combination of aperture, shutter speed) to use. When you shoot in Av, the light meter analyses the scene, takes a look at which aperture you chose, and selects the shutter speed it thinks is the right one. When you shoot in Tv, the opposite, it tells you which aperture to use for the right exposure.
When you do exposure compensation, you are trying to override what the light meter thinks. For e.g. your snow scene. Because snow reflects more light, the light meter will tend to underexpose. You know that'll happen, so you dial in a +1 exposure compensation. Now you're telling the camera, hey I don't trust you, I want you to increase exposure by 1 stop. Meaning, if the camera meters f4.0, 1/60s, after you do +1 compensation, the camera will snap at f4.0, 1/30s instead.
So exposure compensation and the aperture/shutter combi are closely related; they are not separate entities. So if you follow that logic, in M mode you select the aperture and shutter speed yourself. Means, you totally ignore the meter. The meter still shows you what the metering thinks though, by showing you +how much and -how much on the exposure bar. That bar tells you that if you take at the current combi of aperture and shutter speed, how much different will it be from what the light meter thinks. But remember, light meter is not always right. That's why some people use M mode instead.
So in M mode, it is senseless to use AE lock. Why? Cos there is no AE, you are determining the exposure yourself by selecting the shutter speed and aperture yourself!
I hope this explanation is clear enough. If your still don't understand, I really don't know how to help already. And please TRY to understand how things work rather than blindly remembering steps. All those rules you got from the net, like for what situations use +- whatever, are all very rough rules. It helps better if you understand the concept behind exposure, the reason and theory behind why +- so much, and do your own experimentations and trials. This advice applies everywhere, esp in science and engineering: understand what you are trying to do, rather than following instructions blindly.
Please practice and practice before the wedding and know exactly what to do. If you're not confident, I'd suggest you turn the knob to the little green box to avoid disappointment from your friend.
Good luck
