That is an awful, tedious video, and for Gimp 2.8. I should delete it.
However, a more recent, short description here, using brushes as an example:
https://www.gimp-forum.net/Thread-Set-u ... ng-brushesOther resources are similar, zip collections of brushes / patterns / gradients. Scripts, zip individually Scripts register in the Help menu. Patterns in the Patterns dock, Brushes in the Brushes dock....etc
Plug-ins. Since these load when Gimp is started, not supported.