This will take you to the Startup Disk Manager, where you should be able to see the USB drive. To boot from the disk, you need to hold down the option key when you hear the boot chime. Now remove the USB drive and insert it into the Mac computer.
Part 4: Boot Mac from macOS USB Drive for Installation.Home Mac OS Windows 7 bootable USB How to Create macOS Bootable USB on Windows 10/8/7 PC