Once in the command prompt, there are usually 3 drive letters available: X, C, and D. To open a DOS window, press fn-Shift-F10 (or just shift-F10) or click Repair Computer->Troubleshoot->Command Prompt (if available).
When Windows 10 starts up, it will prompt for installation of Windows 10.
Note: the InstallWindowsUEFI variable is cleared at each reboot, so you will need to set it again if you do not select the USB Flash Drive. Insert the USB flash drive if it is not inserted, reboot, and select the EFI volume from the startup selector. Run the following command and enter the admin password when prompted:
The $WinPEDriver$ folder is important because it contains the drivers for Windows to boot successfully from the USB flash drive and the hardware on that Mac. Once the flash drive has been created, it should look like this: On the USB flash drive, open the $WinPEDriver$ and remove the IntelMEI folder.
To install Windows, make sure that the drivers are valid, and restart the installation” message.
It is relatively straightforward to create a bootable USB Flash drive to boot to the Windows 10 installer and open up a DOS prompt for troubleshooting. To troubleshoot an issue with Windows 10 (especially boot-related issues), it can be handy to boot into Windows 10 not installed on a Boot Camp partition.