IMPORTANT: The contents of the drive will be erased after creating a bootable installer drive. In fact, USB drives with larger storage, like 32 GB to 64 GB, tend to show better performance. If you need to create a bootable USB drive of macOS High Sierra, 16 GB USB flash drive is suggested. You should have a USB drive with at least 8 GB of storage and insert the USB drive into your Mac. Step 2 Get A USB Drive with Sufficient Storage Note: After downloading the Mac OS installer, do not install the OS but quit the installer. To download the installer of macOS Sierra, go to Apple Support. However, Apple has decided that macOS Sierra and later will no longer be listed in Mac App Store's Purchased. To download the older Mac OS X version, you can go to App Store > Purchases to download the Mac OS X El Capitan, Yosemite, Mavericks that has been previously downloaded.
To install the latest Mac OS, for example, macOS High Sierra, you can search and download the installer from App Store. The first thing to do is to download the Mac operating system that you need. The most recommendable way to create a bootable install USB drive for Mac OS is using 'createinstallmedia' Command with Terminal application. Use 'createinstallmedia' Command in Terminal
