An automatic Table of Contents relies on Styles to keep track of page numbers and section titles for you automatically. Microsoft Word can scan your document and find everything in the Heading 1 style and put that on the first level of your table of contents, put any Heading 2’s on the second level of your table of contents, and so on.
If you want an automatic table of contents you need to apply the Heading 1 style to all of your chapter titles and front matter headings (like “Dedication” and “Acknowledgements”). All section headings within your chapters should use the Heading 2 style. All sub-section headings should use Heading 3, etc....
If you have used Heading styles in your document, creating an automatic table of contents is easy.
The table of contents is a snapshot of the headings and page numbers in your document, and does not automatically update itself as you make changes. At any time, you can update it by right-clicking on it and selecting Update field. Notice that once the table of contents is in your document, it will turn gray if you click on it. This just reminds you that it is a special field managed by Word, and is getting information from somewhere else.
The video below shows how to make your Table of Contents a little easier to read by formatting the spacing between items in your Table of Contents. You may recognize the "Modify Style" window that appears, which can serve as a reminder that you can use this window to modify more than just paragraph settings in the ToC. You can modify the indent distance, or font, or tab settings for your ToC, just the same as you may have modified it for Styles.
By default, the Table of Contents tool creates the ToC by pulling in Headings 1 through 3. If you'd like to modify that -- to only show H1's, or to show Headings 1 through 4 -- then go to the References tab and select Custom Table of Contents. In the window that appears, set Show Levels to "1" to only show Heading 1's in the Table of Contents, or set it to "4" to show Headings 1 through 4.
You'll quickly realize that all of the automatic Lists and Tables need to be updated occasionally to reflect any changes you've made elsewhere in the document -- they do not dynamically update by themselves. Normally, this means going to each field, right-clicking on it and selecting "Update Field".
Alternatively, to update all fields throughout your document (Figure/Table numbers & Lists, cross-references, Table of Contents, etc...), just select "Print". This will usually cause Word to update everything in anticipation of printing. Once the print preview window appears, just cancel and double-check that it updated things.