Typically one would boot from the flash drive. Generally, one will have to boot their computer (turn on computer and hit the correct key Ex: F10)and enter BIOS and change the boot order so the the system boots from a USB before the hard drive. Remember to change the boot order when you are finished.
1. Turn off computer (or restart)
2. Power on computer
3. Hit required button (in most cases F10)
4. Search around for something like "Boot order" or "Boot device"
5. Modify the list or order by so that the USB device is first
6. Plug in USB drive
6. Save and exit
8. Watch the screen, on some computers user input is required for booting from USB devices
9. Install windows
N. Windows finishes installing
N+1. Remove USB device
N+2. Re-enter BIOS and change boot order as you see fit (Hard drive, CD, USB) similarly as you did in steps 1 through 4
Hope this helps.
Edited by jman242, 09 February 2015 - 09:23 AM.