A MIDI keyboard is any digital piano or keyboard that can tell a computer which keys you press, usually through a USB cable. Most digital pianos made in the last fifteen years can.
Playing on your computer keyboard
The middle row of letters plays the white keys, starting from A, and the row above plays the black keys, the way most music software lays it out. Press [ and ] to move down or up an octave. MIDI.PLAY moves the keys to fit the song on its own when it needs to.
It's a good way to try a song. For anything with two hands or more than a few notes at once, a real keyboard is much easier.
Playing on a MIDI keyboard
See how to connect a MIDI keyboard.
Next questionHow do I connect a MIDI keyboard or digital piano?