@Love4sound follow this step.
While inside Kodi, and in movies section,
1. Click enter files section
2. Click files
3. Click add videos (sometimes step 2 above is not required).
4. Click browse and go to your desired path under your connected hdd. Your hdd should be listed under external storage.
5. Press ok
6. You may give a suitable name. Kodi will default to folder name.
7. Press ok
8. You should be presented with a settings screen. Select the option that the directory contains movies and change other settings as per preference. I only change to get imbd rating.
9. Press ok.
10. You should start the movies section getting filled with movie catalogues.
11. You can reapeat above steps to add multiple folders.
12. You can follow same steps for music and tv shows. Only ensure you select content as tv shows or music in step 8 above.
13. Lastly, ensure that in Kodi main setting (cog wheel in upper left screen), under media settings, the update media library option during startup is enabled for all videos, music and tv shows.
Hope this helps.
Cheers
Siju