Command (⌘)-R: Start up from the built-in macOS Recovery system. Or use Option-Command-R or Shift-Option-Command-R to start up from macOS Recovery over the Internet. macOS Recovery installs different versions of macOS, depending on the key combination you use while starting up. If your Mac is using a firmware password, you’re asked to enter the password.
Shift (⇧): Start up in safe mode.
N: Start up from a NetBoot server, if your Mac supports network startup volumes. To use the default boot image on the server, hold down Option-N instead.
T: Start up in target disk mode.
Command-V: Start up in verbose mode.
Eject (⏏) or F12 or mouse button or trackpad button: Eject removable media, such as an optical disc.