A USB webcam is a camera that connects to a computer, usually through plugging it in to a USB port on the machine. The video is fed to the computer where a software application lets you view the pictures and also transfer them to the Internet.
A LED or Light Emitting Diode is a Semiconductor two terminal(Pin) component, the two terminals are (+)Positive and (-)Negative. The voltage is applied to positive terminal and negative terminal should be ground light is emitted. Here we are using 12V LED so the maximum Voltage for positive terminal is 12V and minimum is 3V. If we use anything above 12V the LED will get short circuit.