Plug the PC straight into the Master18's USB port and choose the Master18 under MIDI output (Windows lists it as DROID X7 MIDI). The Master18 USB switch must be at the right position for USB MIDI (left = USB stick mode, middle = off/reloads patch). For note input, plug a USB keyboard such as the KORG nanoKEY 2 into the computer and choose it under MIDI input; notes are snapped to the selected scale. Web MIDI needs Chrome or Edge on https or http://localhost (e.g. python -m http.server then open http://localhost:8000). Firefox asks for a site permission first.
Steps: click = on/off · right-click or Shift+click = select for editing · mouse wheel = note ±1 scale degree on melodic tracks (Shift = octave) · Alt+click = tie/slide on melodic tracks. The editor under each track changes only the selected step; drum tracks show hits and trigger controls instead of notes. Notes snap to the selected scale on entry, transposition and scale changes. Space = play/stop.