Okay, so you don't have an optical drive? Interesting. You could always use a USB optical drive if you have one laying around (I doubt you do though).
Fortunately you CAN install Windows with a USB bootable flashdrive. Did you buy a version of Windows 8/8.1 yet? If so, did you buy it online? If you did it should have a link to download a .ISO file, if you have a hardcopy (like a CD) you can make an ISO out of that CD on another computer.