You can route Parts to either or both CV/Gate ports using the Part Settings view (to enter this view, press Shift+Sessions).
Routing Parts this way sends all note information to the specified port(s). MIDI notes 24 to 108 will map into a CV pitch voltage range of 0-7V. Notes outside this range will clamp to the maximum or minimum voltage.
CV/Gate is only capable of monophonic communication, so the polyphonic stream of notes from the sequencer, keys, and MIDI will convert to a mono stream using the most recently played note. The Gate port will remain high (open) while a note is active. When you release all notes, the gate signal will fall back to low (closed).
When a part routes to a CV/Gate port, it will also be able to control the respective Mod port. Each Mod port is set to respond to a single CC number, as configured in the Global Settings (see SL MkIII Global settings menu/Cv mod 1 CC and CV mod 2 CC).
When a part that routes to a CV/Gate port outputs this CC number via the surface, the sequencer or MIDI, it will output as a voltage in the range of 0 to +5V from the Mod port.