Create a bootable USB installer for macOS
If you would like to perform a clean install of macOS Sierra or update multiple machines, it's a good idea to create a bootable USB installer.
Step 1 - Download macOS Sierra from the App Store
Download macOS Sierra from the App Store. The installer program should automatically open after the download completes. Do not proceed with the installation, cancel and close it.
Step 2 - Format the USB Drive
Plugin the USB drive, launch the Disk Utility app, select your USB drive on the left and click the erase button. You can leave the default name Untitled since it will be renamed automatically in the next step. If erasing the disk fails on the first attempt, try it again and it should work on the second attempt.
Step 3 - Create the Install Media
Run the program to create the install media from the Terminal.
Reboot into the Installer
Hold down the option key immediately after you restart the computer. Then select the USB drive with the installer on it and the macOS Sierra installer will start.