For instance, suppose you were formatting headings. Your current text is Times Roman size 12. You want to change it to Helvetica size 18, with half a line above the paragraph. If you did that manually, you would need to go through three steps. A style tag will do everything at once.
Word offers several preformatted style tags, but their heading fonts differ from their text fonts.
If you like to keep everything in the same font, you can create your own style tag. Word will then ask you to give your style a name. When naming your headings, you want to ask yourself whether you will use them in the table of contents. If you are, you want to go back to the first screen and use the existing style names. If you are creating a new one, type the name of your style in the blank.