You can set the shift point by holding the button down till the light comes on green, then revving to 1/2 the desired shift point, and pushing the button again.
Shift is indicated with a Green light. Moderate knock with Amber (Red + Green together), and Heavy knock with Red.
It's not possible to hook it up without the tach signal - it needs to know the RPM so that it can "filter" background engine noise. Otherwise it would just be lighting up constantly at higher RPMs like a KnockLink. The light is calibrated by letting it record engine noise by reving to idle, half of redline, and near redline in turn - the sensor then interpolates the points to come up with an engine noise "curve" that it uses to distinguish between background noise and knock events (a knock sensor is just a microphone, after all). The sensitivity can then be adjusted up or down from there.
It's a pretty trick unit. If you have a DTEC, it'll supply Tach and Knock level inputs to be logged or displayed as well.