The input gain, the law and the attack/decay time constants are all settable. The graph shows the compression 'law'. To add a point to the curve, click on the curve and a new point will appear, to move it, click on a point and drag it, to remove one drag it off the graph.
In this case, the input gain is set to +1dB, the law has reduced the output signal to zero when the input is below about -50bB (noise gate), then provides some boost at low levels and compression at higher levels. The attack time constant is 1mS (fast) and the decay is 1S (slow).