How to adjust camera's exposure, brightness or contrast?

Exposure, brightness, contrast, ... adjustments are camera specific and are provided by the camera drivers or the camera configuration web interface. ContaCam just shows what is given by the camera manufacturer.

For USB camera / capture card

Go to Camera Advanced Settings - General Tab and press the General Settings button to display the driver provided dialog.
Note: some drivers do not store the set values; ContaCam can do nothing about that, please contact your camera / capture card maker.

For IP camera

Go to its web interface (accessed through http://camera_ip_address from your web browser).