Virtual Piano
The on-screen piano, and using the computer keyboard as a MIDI input.
The virtual piano is an on-screen keyboard for playing the selected track’s instrument.
Computer keyboard as MIDI
On a hardware keyboard you can also turn the computer keyboard into a MIDI input with Cmd + M. The letter and number keys then play notes in a piano layout, and - / + shift the octave down and up. While this mode is active, unmapped keys are ignored so they don’t trigger their usual shortcuts. See Keyboard Shortcuts.