You can create Custom Themes and Custom Style Sets. The Styles shown in the Style Gallery can be a Custom Style Set.
I believe you want to Understand Themes and the Style Sets you'll find on the Design Ribbon. Also how the Colors and Fonts can affect your document from the Design Ribbon. Most people do not understand that is where the default font/typeface is/can be selected. The default Font for Styles can be changed in the Style itself, but that would defeat the function of the Design Tab.
The Style Sets there also show how easily a document can be changed.
A Custom Style Style set. If you go through creating (you would really Copy and Modify) a custom Style Set, you first find that Word will create a new Document Template to store the set! Take note of the default folder.
You can add more styles to the Gallery from the Style Set, but you need to make sure you add to the Current Document and New Documents Based on This Template to ensure consistent behavior.
Add Styles to a Style Set? That would be super special rare case considering all the predefined styles that already exist.
There is a Macro at StackOverflow that can list most the styles in the Current Style Set and the parameters. The macro as published, excludes List and Table styles.