Then, the downloaded file, opencv-3.2.0-vc14.exe is extracted at C:\opencv as a folder called opencv320. Visual Studio 2015 IDE is downloaded from https://www.visualstudio.com/downloads/ and install. The following steps are tested on Windows 10 64 bit using Visual Studio 2015 and OpenCV-3.2.0. For other versions, the precedures are similar.
At first OPENCV_DIR is declared as an enviroment variable. Run 'Command window' in administrator mode by right clicking start menu and choosing command prompt (admin). Enter
setx -m OPENCV_DIR C:\opencv\opencv320\build\x64\vc14