sizcoz glad you got it working!
I do remember having that issue with installing an APK from the file explorer a couple of years back, the only way I could get it to work on that device was to use a 3rd party file manager.
It seems to install directly from chrome on my current test device (oneplus 3), but I guess the mileage may vary a little. I've also had success installing directly from google drive, which is helpful if your working on your desktop and you want to test a build quickly.
If you were having trouble accessing the zipalign tool I believe it's hidden away inside the AndroidSDK, so you can't access it without adding it to the PATH.