You can apply numbering to a paragraph manually or with a paragraph style.
If you want numbered headings, use Tools - Chapter Numbering, instead of numbering manually.
To apply numbering manually, click in the paragraph, and then click the Toggle Ordered List icon on the Formatting bar, or use the dropdown box on the icon to select a numbering format.
You cannot apply manual numbering to paragraphs that are listed under "Special Styles" in the Styles window.
To add selected paragraphs to an existing list, use Format - Lists - Add to List.
Paragraph Styles give you greater control over numbering that you apply in a document. When you change the list style assigned to a paragraph style, then the numbering format in the list style is applied automatically to all paragraphs using the paragraph style.
Choose View - Styles, and then click the Paragraph Styles icon.
Right-click the paragraph style that you want to apply numbering to, and then choose Modify.
Click the Outline & List tab.
In the List style box, select the list style to apply.
Apply the paragraph style to the paragraphs that you want to add numbering to.