If you create documents in which the various text elements always appear in a particular order, you can "chain" them together so that when you press Enter to end a paragraph formatted with one style, Word automatically applies the second style to the next paragraph. Linking styles in this way can save you many trips to the Style list in the Formatting toolbar.
For example, let's say you're creating an instruction manual in which each topic is composed of a heading, an introductory paragraph, and then a numbered list of steps. And let's say you've created styles named Topic, Intro, and Steps for these three elements. You can chain the styles together so that Topic leads to Intro, Intro leads to Steps, and Steps leads back to Topic.
When you're creating or modifying a style, you can specify a style to follow by choosing it from the Style for Following Paragraph list in the New Style or Modify Style dialog box.