Choose the USB drive from the boot menu.
This does install the OS; it extracts the "Install macOS Sierra" application into your Applications folder. Creating a Bootable USB Installer
Ensure you are using Safari, as other browsers sometimes struggle with Apple’s direct download links for legacy software.
Open and format the drive as Mac OS Extended (Journaled) with a GUID Partition Map . Name the drive "SierraInstaller".
Navigate to the official Apple "How to download macOS" page.
Open and paste the following command: sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/SierraInstaller --applicationpath /Applications/Install\ macOS\ Sierra.app
Press , type your admin password, and wait for the process to complete. Installing macOS Sierra from the DMG
