Fundamental VCF is a Voltage Controlled Filter
It can act as a LowPass and HighPass Filter at its outputs, marked LPF and HPF. LPF is -24dB/Oct and HPF is -12dB/Oct.
Cutoff frequency is set by the FREQ Knob. Its maximum values is 8400 Hz while minimum frequency is 15 Hz. FINE controls fine-tuing of the filter Cutoff.
Cutoff can be modulated by CV signals using the FREQ input port and the associated FREQ CV attenuator. (how much signal is passed to the Cutoff Frequency),
Resonance works the same,it is controlled by the RES Knob and can be modulated using the RES input, which has no attenuator. Resonance can be set to its maximum and the filter can be set in self-oscillating mode (e.g.it behaves more or less like an oscillator)
The DRIVE knob allows to add gain to the filtered signal.