Launch Reaper.
Click the "VU" meter on the track.
Click "MIDI Input." Select "Virtual MIDI Input" from the drop-down menu to make the "QWERTY" keyboard your MIDI input device.
Connect a MIDI controller to any available USB port.
Launch Reaper.
Click "Open" and select "New Track."
Click the "VU" meter on the track to select an input device. Click "MIDI Input," "All MIDI Inputs" and select your specific MIDI input device from the drop-down menu.