When you open RUFUS there's a section called CREATE A BOOTABLE DISC USING, here choose ISO IMAGE from selection menu, than there's an icon of a cd drive next to it click it and choose you ISO (assuming the USB is plugged in). RESTART your PC then when it boots, you must notice an F2 or F9 or F12 command that would take you to BOOT DEVICE, if you can find it, choose BOOT FROM USB (if you are using a DESKTOP when you first turn on the PC press DELETE to enter the BIOS menu than you navigate until you find BOOT MENU OPTIONS). The idea is to set your PC to detect the USB when it restarts then the process is just like installing from a DVD/CD