You can accomplish this by either using Disk Utility or Boot Camp Assistant. You'll need to make room on your hard drive for Windows 10 which requires partitioning your drive. You Mac's internal SSD drive is devoted to OS X. My favorite freeware version is 'ISO to USB.'

If you have access to a Windows machine (ironic catch 22) you can use several ISO to USB programs.

If you have backed up your Mac and are comfortable using UNIX commands in Mac Terminal then you can look at Paul Horowitz's OS X Daily article on How to Copy an ISO to a USB Drive.

ISO and then transfer it to your USB Flash drive.

If you have a DVD version of Windows 10 you'll need to convert it to an.

I did not have success with this method or using Disk Utility's ISO to USB function.

Boot Camp Assistant is installed on all Macs and can be found in your Utilities folder. It copies your Windows 10 ISO file to the USB Flash Drive in a format that can be booted from. If your Mac's Boot Camp Assistant is NEWER than 5.1.4 you can try to use it to create your install disk.Using a USB Flash Drive larger than 32 GB may result in the extra space being unused (Fat32 can only format up to 32GB). You'll need an empty 4GB or larger USB Flash Drive. Unfortunately you can't simply drag and drop the files because the USB Flash Drive needs to be formatted into a format that allows it to boot your Mac. If you downloaded your copy of Windows 10 you'll need to correctly copy it onto a USB Flash Drive. If you purchased your copy of Windows 10 on a USB Flash Drive you can skip to this step. Be sure to only download Windows 10 from the Microsoft site to avoid malware. I was unable to enter a Windows 7 or 8 product key in the Windows 10 installer (it won't ask if it auto detects Win 7 or 8 previously installed). You can also download Windows 10 as a free download from Microsoft, but you will need a valid Windows 10 product key to activate at some point. I was unable to use Disk Utility or Boot Camp Assistant to properly create the Windows 10 USB Flash Drive from my OS X 10.10.4 Mac as of August 2015. iso disc image to a 4GB or larger USB Flash Drive, and this step is best done from a Windows computer. Purchase Windows 10 as a download from the Microsoft Store or Amazon. If you buy the Windows 10 Pro version it includes the installers for both the Pro and Home 64 bit versions. Purchase Windows 10 on USB flash drive from the Microsoft Store, Amazon or a local computer reseller. Microsoft makes it easy for existing Windows 7 and 8 users to get a free version of Windows 10 from within Windows, but for a new installation of Windows on a MacBook that has never had a copy you'll want to look at the following methods:

Making bootable windows 10 usb on mac