Assuming you are asking about an active stylus:
An active stylus is a pen-like device that uses battery power to produce electromagnetic waves. The waves interact with a digitizer in the tablet or laptop, allowing the user to write or draw on the screen with greater accuracy and control than their finger could provide.
To activate an active stylus, simply press the button on the side or top of the pen. This will usually turn on a blue light on the tip of the pen, indicating that it is ready to use. Then, touch the tip of the pen to the surface of the screen. The cursor should move as you move the pen across the screen. If it does not, try restarting your computer or reinstalling your drawing software.