Word 2016's heading styles are numbered Heading 1, Heading 2, on down to Heading 9. You use them to identify different parts of a document, but they also take advantage of other Word features. You're not stuck with using Word's preset heading styles; you can create your own.
For example, text formatted with a heading style appears whenever you use the vertical scroll bar to skim a document. Headings can be expanded or collapsed, as part of Word's Outline feature. Headings appear in the Navigation pane when you search for text. They can be used when creating a table of contents.
The key is to set your own heading style's outline level: In the Paragraph dialog box, use the Outline Level menu to set the heading level: Set Level 1 from the Outline Level menu for top-level headings. For the next heading level (subheading), choose Level 2, and so on. These paragraph formats are used by Word's document organization tools, such as the Navigation pane and table of contents command.
Update your heading styles to reflect the proper Outline Level paragraph format:
Summon the Styles pane.
The keyboard shortcut is Ctrl+Shift+Alt+S.
Click the New Style button.
The button is shown in the margin. Click it to see the Create New Style from Formatting dialog box, as shown.
Type a short, descriptive name for the new style.
Ensure that Paragraph is chosen for the style type.
Choose an existing style as a base from the Style Based On drop-down list.
Use this step to save time. If the style you're creating features a lot of the same formatting as an existing style, choose that style from the list. The formats from that style are copied over, letting you build upon them or reuse them in a different way.
You can choose a preset Heading style as your base.
Use the controls in the dialog box to set the style's format.
The Create New Style from Formatting dialog box is brimming with style command buttons.
Use the Format button in the dialog box's lower-left corner to apply specific formatting commands. Choose a category from the button's menu to see a dialog box specific to one of Word's formatting categories.
Click the OK button when you're done.
Heading text is typically only one line long. Larger font sizes are usually selected. The Space After paragraph format is frequently applied.
Word's predefined Title style isn't a heading style.