NIKON EXPERTS - EXP COMPENSATION AND WHITE BALANCE?

I was wondering if anyone can tell me where this "exposure compensation button is? On a nikon d300? And would some kindly explain what it is and why? I understand it a bit but a nice clarification would help. Also, the setting on white balance on nikons is default… I fail to see its purpose to change it? I know that using tungsten indoors helps etc but does it Really make much difference?
many thanks

Added (1). Ok… Other then M mode. I use manual mose all the time so surely I can just add a stop my self? As opposed to using this compensation button?

Where it is… At about 4 o'clock in relation to the on/off switch with the black/white +/- on it.

What it is… So you can override the camera's selection of exposure in exposure modes other than M.

The quality of light changes at different times of the day/indoor/with flash so the white balance can be used to compensate for it. If you use RAW you can do that in processing.

The wrong white balance can give photos a colour cast, e.g. Too blue later in the day for example, if daylight (blue sky) is used.

Edit
Yes, if you use M mode then you don't need exposure compensation, you just set a different exposure.

The EV button (+/-) has NO effect if you are in manual. It is for adjusting exposure if you are in A or S mode.

The white balance I generally leave on Auto - my D300 gets it right most of the time. BUT I shoot in raw in which case it's easy to adjust in post anyway.

You will notice a difference - if you set it to tungsten (in daylight) you will get a blue colour cast over the image, similarly if you shoot in fluorescent, you will get a pink colour cast - this can be used for effect.

All above answers good. Watch out for Manual mode and Auto ISO. Auto ISO will function in manual mode which means the EV compensation will also work when in Auto ISO mode. Don't know why Nikon doesn't have a disable Auto ISO when in manual mode check box.
Generally, EV compensation is used in PAS modes.

White balance is extremely important if shooting JPEG. Auto does a pretty good job, but I find shooting in theater settings, mix lighting, under odd lights, like fluorescent or sodium, I need to custom white balance or use one of the presets. If you shoot raw, you can deal with and color cast in post processing. By locking down your WB, you won't get slight color shifts when shooting in the same area. Also, some shots you want to set the WB for artistic effects like using Cloudy when shooting sunsets (makes the oranges deeper). You can also use WB for artistic purposes when shooting mixed lights.