Being a calibrated precision tool, a torque wrench is used for applying a known amount of load to any bolt or nut. The length of the wrench will determine the amount of force required to reach the desired torque value. (torque = force x length)
E.g. If your torque wrench is one foot long and you apply 30 pounds of force on the handle, you are applying 30 ft. lbs. of torque on the fastener you are tightening.
If you torque wrench is two feet long, and you apply the same 30 pounds of force on the handle, the longer tool will increase the leverage effect and multiply torque, applying 60 ft. lbs. of torque to the fastener.