When we talk about modifying a style, it’s always worth talking a little bit about templates. Any time you change a style or create a new style, you have the option of adding your changes to the document's template. By doing so, you’re permanently altering the style in this template (unless you change the template later), and you’re making the style available to other documents that use this template.
What's the template?
The template is the file whose styles your document is based on. It exists as a separate file that works in tandem with the document — but it stays in the background. For example, every time you open a new document in Word, you get a blank document to type in. All its default formatting is dictated by Word’s default template, normal.dotm (the "t" in the file extension is for templates).
If you save style changes to the template, the modified style is permanently changed for all documents that use this template. So, for example, if you change the font size and color of a Heading 2, and you apply those changes to the template normal.dotm, every time you open a blank document, your heading will have the new font size and color. If you don't save the change to the template, the modified style is saved only to the current document. In the practice session, you'll see how to save changes to the template and how to see what template your document is based on.