Open Reaper and click on "New" to open a new project.
Select "Track" and then "Insert new track" to add the first track to the sequencing window.
Click on the tab in the master fader and select "Show FX inserts when size permits" to display the inserts in the first track.
Click on an insert slot to open the FX browser. Select "VSTi" to open the list of virtual instruments and double-click on an instrument to add it.
Right-click on the meter and then select "Monitor Input." Right-click again and select "Record: Input." Right-click once more and select "Open Labs MIDI Driver" from "MIDI Input."
Click on "R" to arm the track for recording.
Right-click the metronome settings tab to customize the metronome playback options. Select "Input Quantize" on the input meter to enable automatic quantization during recording.
Click on the "Record" button on the transport panel to begin recording. Press "Play" to listen.
Repeat this process to add more tracks and instruments to the piece.
Click on "File" and select "Save as" to save the completed project.