When I attached another camera through USB port, web cam turns on and I could not use the one I want to. I want to have webcam turned off temporarily

If you're looking to disable the "on board" webcam, then just open the program and look for the "settings" or "options" item. From there you should be able to disable it.

If you are having problems finding that option, tell us the make and model of the laptop so that we might be able to help further.