Arranger keyboard mode
If you have a Midi keyboard connected via Midi IN, you can use it as a (pseudo) arranger keyboard: JJazzLab will recognize the chord symbols played and update the backing track accordingly.
First connect your Midi keyboard to a Midi IN device (see the Midi panel of Options/Preferences).
Create or open a song, then select a song part. The song part will be used by JJazzLab to know which rhythm and which rhythm parameters should be used during the arranger mode session.
Display the Arranger window (menu Window) and press its Play button: music should now follow the chords you play on your keyboard.
Only the notes received below the split note are used for chord symbol recognition.