What are Styles?
Built-in styles are combinations of formatting characteristics that you can apply to text to quickly change its appearance. For example, applying the Heading 1 style might make text bold, Arial, and 16 point, and applying the Heading 2 style makes text bold, italic, Arial, and 14 point. (Those are examples; exact formatting characteristics depend on Word's default settings and those you might have chosen for yourself.)
Here are the top 5 reasons to use Word Styles:
1. Styles application means easy Table of Contents generation
The easiest way to create a table of contents is to use the built-in heading styles. You can also create a table of contents that is based on the custom styles that you have applied. Or you can assign the table of contents levels to individual text entries.
Mark entries by using built-in heading styles
Select the text that you want to appear in the table of contents.
On the Home tab, in the Styles group, click the style that you want.
For example, if you selected text that you want to style as a main heading, click the style called Heading 1 in the Quick Style gallery.
If you don't see the style that you want, click the arrow to expand the Quick Style gallery.
If the style that you want does not appear in the Quick Style gallery, press CTRL+SHIFT+S to open the Apply Styles task pane. Under Style Name, click the style that you want.
2. Styles cascade and so when you make one change to a document you have made them all
Instead of using direct formatting, use styles to format your document so you can quickly and easily apply a set of formatting choices consistently throughout your document.
For more information see Style basics in Word
3. Styles allow you to use Outline View
When you enter your first top-level outline entry, Word automatically formats it with a built-in style, Heading 1. As you continue to build your outline by adding subordinate and body levels, Word in turn continues to apply the appropriate built-in style to each heading and body text entry. In this way, your outline levels (Level 1, Level 2, Body Text, and so on) are directly tied to built-in heading styles (Heading 1, Heading 2, Normal, and so on).
While you can manually change the formatting of text in your outline, veering away from the built-in styles that Word offers can result in some outline entries not being displayed correctly. So if you want to change formatting across your document, you might want to do so in another view, such as print layout view, once your outline is complete.
On the opposite end of the spectrum, if you find extra formatting distracting, you can display your entire outline as plain text by clicking Show Formatting on the Outlining toolbar.
4. Restrict formatting changes
You can lock down styles in a document to make sure that others don’t apply direct formatting and change your document creating a huge mess.
Restrict or permit formatting changes
5. Templates are much more efficient and kinder to others if they're based on styles
A template is a Microsoft Office document that’s been designed with pre-existing themes, styles, and layouts, which has placeholder information instead of real content.
Templates are a great way to save time and create consistent Office 2010 documents. They are especially valuable for types of documents that you use frequently, such as weekly presentations, application forms, and expense reports. If possible, you want to use a file that already has the look and feel that you want, with placeholders that you can change to tailor it for your current needs. That’s what a template is—a file where the hard work has been done for you, saving you from having to start with a blank page.
In addition to the templates that come with the program, you have free access to all the templates on Office.com
Style basics in Word
You can also get help from the Microsoft Community online community, search for more information on Microsoft Support or Windows Help and How To, or learn more about Assisted Support options.