Before you can install Arch Linux, you need to get the ISO from the Arch Linux website. Once you have the ISO from your mirror of choice you should install Rufus (if you're on windows) and use that to copy the ISO to your USB drive. Then boot into the USB drive that you have just put the ISO's files onto (steps vary). Once you've booted in do these commands to ensure the rest will go smoothly.
loadkeys (your locale, google that.)
ping -c 3 google.com