Blender can store assets in a custom folder in your PC using the "Custom / default" path set into File system paths in user Preferences. This library can contain all your assets available for any scene. Hence I will refer to this as the "global library".
Blender also gives you the option to embed your asset library in the current .blend file you're working on. This is the "Built-in / current file" asset library.
If I open a .blend file with library assets, how can I transfer them to my "global" library? Do I just copy/paste the .blend to the windows folder (custom/default)? If so, how to categorize my assets?