Downloading windows 10 on Mac

I am trying to download windows 10 on my Mac running on os x yosemite 10.10.5 because i have heard it is doable.

I have downloaded the iso

I have a usb ready

I have gone on to bootcamp assistant done that phase but then an error keeps popping up saying it couldnt make it a bootable device or something.

Where am i going wrong?