The Brightness & Contrast effect adjusts the brightness and contrast of a layer. It adjusts all pixel values in the image at once. It does not affect individual channels, or separate highlights, shadows, and midtones. The entire image is affected. The Brightness & Contrast effect is the easiest way to make simple adjustments to an image.
To apply it, select your footage and go to Effect, Color Correction, Brightness & Contrast. You can affect the brightness or contrast of your footage separately. A value of zero means that no change has been made to your footage. You can change the values in a positive or negative direction. Positive values will make an image brighter or provide more contrast. Negative values will darken an image, and reduce the contrast.
Ultimately, this is one of the weakest color correction tools After Effects has to offer. You’re far better off using Curves or Levels, as you can affect the highlights, shadows, and midtones for individual channels. But if your footage is only in need of some very minor tweaking, Brightness & Contrast might work just fine.