The terminal erases the USB, copies the hidden BaseSystem.dmg , and makes the drive bootable.
*Note: macOS Sierra is no longer receiving security updates from Apple. Ensure you have a good antivirus and safe browsing habits if you use download macos sierra 1012 dmg file install
Press , type your admin password, and wait for the process to complete. Installing macOS Sierra from the DMG The terminal erases the USB, copies the hidden BaseSystem