I'm trying to create a bootable usb, but the boot and run linux software needs an ISO file according to the instructions on ubuntu help. I have no idea what that is or where to get it.
An ISO file is also sometimes called an image file. It is sort of an archive for CDs or USBs. This is indeed what you need to install Ubuntu.
Go to http://www.ubuntu.com/download/desktop and hit the Download button to get your ISO file.
You will have the choice between the 32 bits and the 64 bits versions of Ubuntu : choose the one that corresponds to your computer.