The torque wrench is used to apply a specified amount of torque to a fastener.
There are various methods used by torque wrenches to indicate that the correct torque has been reached. Some will give an audible signal such as a click or a beep, while others will give a visual signal such as a light or a pin moving or clicking out.
Make sure the threads are clean before tightening the fastener to a specified torque. Any friction will give an inaccurate reading and will affect the compressive force the fastener will apply to the component.
Always handle a torque wrench carefully. It is a precision instrument that will lose its calibration if mistreated.