The structure for WinapiExtension is very simple. There is a include directory, which has a subdirectory WinapiExtension.
Common installation choices would be to copy the framework to a central location, say "C:\WinapiExtension_1.0", and let your compiler know about this directory. Alternatively you could copy the "include\WinapiExtension" directory into the source of your own project.
Once the files are in a place where the compiler can find them, include them like this:
WinapiExtension.h is the main header for the library. It includes all other necessary files.