There should be an icon on your desktop for the webcam, if not try checking in your device manager to see if it is enabled..go to control panel>system>hardware>device manager It should be under the imaging devices.
Did you install the drivers for the webcam? It should have came with the webcam. Otherwise you need to download the drivers from the manufacturer's website. Additionally, the webcam should have came with a manual to walk you through how to use the webcam.