macOS Recovery is part of the built-in recovery system of your Mac. You can start up from macOS Recovery and use its utilities to recover from certain software issues or take other actions on your Mac.
How to use macOS Recovery
- Turn on your Mac and immediately press and hold Command (⌘)-R.
- Release the keys when you see an Apple logo, spinning globe, or other startup screen.
- You might be prompted to enter the login password of an administrator of this Mac, or your Apple ID password, or a firmware password. Enter the requested password to continue.
- Startup is complete when you see the utilities window:
- After starting up from macOS Recovery, select a utility, then click Continue:
- Restore From Time Machine Backup: Restore your Mac from a Time Machine backup.
- Reinstall macOS: Download and reinstall the Mac operating system.
- Get Help Online: Use Safari to browse the web and find help for your Mac. Links to Apple's support website are included. Browser plug-ins and extensions are disabled.
- Disk Utility: Use Disk Utility to repair or erase your startup disk or other storage device.
Additional utilities are available from the Utilities menu in the menu bar: Startup Security Utility (or Firmware Password Utility), Network Utility, and Terminal.
- To quit macOS Recovery, choose Restart or Shut Down from the Apple menu . If you want to choose a different startup disk before quitting, choose Startup Disk from the Apple menu.
If you can't start up from macOS Recovery
If your Mac can't start up from the built-in recovery system, it might automatically try to start up from macOS Recovery over the Internet. When that happens, you see a spinning globe instead of an Apple logo during startup. To manually start up from macOS Recovery over the Internet, press and hold Option-Command-R or Shift-Option-Command-R at startup. Learn more about these key combinations.
If your Mac still can't start up from macOS Recovery, you might need to start up from another disk or volume, or use a bootable installer.
macOS Recovery over the Internet, the Reinstall macOS utility, and the Get Help Online utility all require an Internet connection. If you need to connect to a Wi-Fi network, move your pointer to the top of the screen, then choose a network from the Wi-Fi menu 
in the menu bar.