Highlight a page heading. A context menu will expand automatically. Click Styles on the context menu. Select Heading 1. Repeat for all major pages in your document. For minor pages and sections, select those headings and assign them Heading 2. Heading 2 entries will appear as sub-sections of Heading 1 entries in your ToC. You can also assign additional minor sections as Heading 3, which will appear as subsections to Heading 2s in the ToC.