The output is the input multiplied by the other input, i.e. the output is the product of the inputs. The inputs can be AC (i.e. normal audio signals) or DC (e.g. dynamics side chains etc.). Note that distortion will result if both inputs are AC (audio).
The modulator could for instance be used to allow the amplitude in one signal path to control the amplitude of a signal in another signal path to achieve a level-riding effect. To do this, you would put the controlling signal through a 'meter' to turn it into DC, then apply that to one modulator input, then pass the controlled signal through the other modulator input to the output.
Inputs & Outputs
Two inputs, one output and no control panel or properties.