Connecting an electric piano to a MacBook

FilSto wrote:

It is a Yamaha Portable Grand DGX-640. It doesn’t come up anything on the computer screen

unfortunately it appears that the DGX-640 is not Mac compatible:

if the keyboard has a MIDI-OUT jack you could connect it via a Mac compatible MIDI interface, but not directly through the built-in USB port.

There is a driver available on official website, it should help you connect your Yamaha to MacBook properly: https://usa.yamaha.com/support/updates/usb_midi_driver_for_mac.html

I checked it, and it's compatible with DGX-640.

Which Electric Piano? Does it show up in Audio Midi Setup?

Which Electric Piano? There is a good chance you will have to use the Piano to play Garageband's sounds. Garageband can receive MIDI, but it cannot output it back to your Piano. If you want to record your Piano's sounds, you will have to get an audio interface.