Scroll down and double-click on Disk Utility.
Scroll down and double-click on Utilities.Select Applications from the list on the left side of the window. Click on Finder in your Dock to open a Finder window.Plug the thumb drive or cable for your hard drive into the appropriate port on your Mac.You'll need to start with a clean thumb drive or external hard drive to make it a bootable drive. How to format your external drive for macOS Big Sur
