What were you trying to do when you erased everything? Were you trying to install Windows instead of macOS?
Are you trying to reinstall macOS? If so, and if you just used Disk Utility to erase your startup disk, you might need to get an external bootable drive with macOS. See How to download and install macOS - Apple Support. If you can't reinstall macOS after pressing Command-R at startup, press Option-Command-R at startup instead, then try again. See How to reinstall macOS - Apple Support.
Let us know more information about your situation and we might be able to help. Good luck!