MIDI environment Signal Flow, with DAW software
The basic signal path and flow of control information, is to start with a MIDI keyboard, or surface controller. That device will emit MIDI control signals to either a MIDI device (like an analog synthesizer, with MIDI to CV adaptor) or to a Personal Computer (or laptop/tablet) to record the MIDI commands. The PC runs Digital Audio Workstation (DAW) software to record, edit and playback MIDI command streams. The output of the PC connects to a synthesizer that has compatible MIDI inputs. Some times a musical instrument that has build in keyboard, can be playes by the MIDI commands from a PC or other MIDI controller.
Control Voltage vs MIDI - Daniel Fisher - YTV
The MIDI standard allows equipment from different vendors to work with each other.