You have to mount this file (IOT Core RPi.ISO) (Win 8.1/10 does it automatically with a double-click). Inside is the installer Windows_10_IoT_Core_RPi2.msi, which you perform and follow the steps. After installation, you can unmount the ISO file.Now you have to search for and open IoTCoreImageHelper.exe via the Windows Start Search. There you select the SD card and the path to flash.ffu (this is located under C:\Program Files (x86)\Microsoft IoT\FFU\RaspberryPi2)