If you glance at the Style list occasionally as you're typing a document, you may notice new styles suddenly appearing in the list. By default, Word creates styles for you based on the formatting that you apply in your document. Although this might be helpful for people who don't want to pay any attention to styles, it can be annoying if you want to closely control the styles in your document.
While you're learning about styles, it's a good idea to turn off this feature so that you have to contend only with styles that you've created yourself. You can always turn it back on later if you choose.
To turn off this feature, follow these steps: