If you go into Print Preview, the field will automatically update in the Headers or Footers. Unfortunately, if you also have the field in the main document, (for example, in the coversheet), going into Print Preview won't update it – but printing will, provided that you have Update Fields ticked under Tools + Options + Print. You can also update the field by selecting it and pressing F9. Or you can press Ctrl+A followed by F9 to update all the fields in the main document in one go.
One solution is to format the heading with the style and follow it with a hidden paragraph mark. You should format the text in the next paragraph with a style that is not included in the Table of Contents. A hidden paragraph mark keeps the text together on one line when it is printed, even though it is actually two separate paragraphs. The Table of Contents command picks up only those paragraphs with heading styles and places them into the Table of Contents.
It's also possible to consecutively number list items in InDesign. Create a text frame for your list and click the numbered list button to insert a list. Type your list items, pressing your "Enter" key between items. InDesign consecutively numbers the list automatically; you can change the number it begins with and the style of the numerals. Press your "Alt" key (Windows) or "Option" key (Mac OS) while clicking on the numbered list button to open a dialog where you can modify those options.
Let’s say you want to use roman numerals for the introductory pages, arabic numbers for the main body and lowercase letters for the closing pages. Each of these formats can be selected in the Page Numbering Format dialog box. First, position the insertion point where you want to start using a different page number format. Choose Format > Page > Numbering. In the Page Numbering Format list box, select a format, and then choose OK to insert the page number.
In Japanese, Chinese, or Korean versions, by default, Arabic numerals are used for page numbers. However, if you use the Numbering & Section Options command, you can specify the style of numbering, such as Roman numerals, Arabic numerals, Kanji, and so on. The Style option allows you to select the number of digits in the page number, for example, 001 or 0001. Each part of the document that uses a different numbering style is called a section. For more information on sections, see Define section numbering.
CK Note: Word 2007 - 2013 interface has an different automatic numbering scheme which I have been told is much less subject to corruption. Microsoft Word 2010 Bible by Herb Tyson, MVP. However numbering is still very imperfect in these later versions. I still recommend following Shauna Kelly's step-by-step instructions (see above) if setting up numbering in a template or in a document likely to be heavily edited. If you start without doing this and end up with "spaghetti numbering," fixing it will be a very large chore!