Screenshot of my first synth in VCV Rack standalone free version, featuring a MIDI module taking input from my controller and sending its voltage/octave signal to the corresponding input on a VCO module, which sends its square-wave output to a VCA module, which sets the volume of the signal as it is passed on to the audio output. This on its own creates a continuous tone with a pitch defined by the key pressed on the MIDI controller keyboard and the volume set by the VCA.

Another MIDI output, the gate, is sent to an ADSR envelope module, which then passes its envelope output to the volume control of the VCA module, turning the sound up and down according to the ADSR profile. 

Together, what this shows is that a single key press on the MIDI controller tells the VCO what pitch of tone to generate, and also tells the envelope module to control the volume of the tone during and after the key press. Neat!
Screenshot of my first synth in VCV Rack standalone free version, featuring a MIDI module taking input from my controller and sending its voltage/octave signal to the corresponding input on a VCO module, which sends its square-wave output to a VCA module, which sets the volume of the signal as it is passed on to the audio output. This on its own creates a continuous tone with a pitch defined by the key pressed on the MIDI controller keyboard and the volume set by the VCA. Another MIDI output, the gate, is sent to an ADSR envelope module, which then passes its envelope output to the volume control of the VCA module, turning the sound up and down according to the ADSR profile. Together, what this shows is that a single key press on the MIDI controller tells the VCO what pitch of tone to generate, and also tells the envelope module to control the volume of the tone during and after the key press. Neat!