I am really lost. After the accidental factory reset ( no back up!) I tried to to reinstall the apps from the apk files from the D2-912 drive in My Computer, which still lists ALL the contents of the device, but I was unable. How can I get everything back. I suppose I did the equivalent of formatting a OC Drive, but how do I get the Android system into the device?
Bit confused as to what you did and what you are trying to do. If you do a factory reset, it does not wipe the operating system, only removes your personal settings and files. Why are you asking how to get the Android system into the device?
The applications you can just re-download from the Google Play store. Installing from the APK files you may need to root your device or at least allow unknown sources to install items in the security options.
If you need to install APKs, try putting them into the downloads folder of your device, then find it in a file manager and click on it. You will need to turn on unknown sources in settings. Instructions for unknown sources: http/gs4.wonderhowto.com/forum/enable-unknown-sources-android-install-apps-outside-play-store-0150603/