To launch Hiren's BootCD from a USB flash drive, the boot order in the computer's BIOS must be configured to boot from the USB drive first. Then, the USB drive must be formatted, Grub4Dos installed to allow booting from it, and the files from the Hiren's BootCD copied over. When complete, the USB drive will contain all the necessary files and be bootable to launch Hiren's BootCD utilities from it.