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Your Contents. In A Table.
When you add a table of contents to your document (TOC), Word automatically searches through it looking for items that are marked for use in the TOC. Certain elements, i.e. headings, are marked this way by default but you can also mark other elements manually.
The facility to add a table of contents is not on the insert tab as you might expect. Position the cursor where you want to insert the TOC and click References > Table of Contents > Table of Contents and a gallery of built in TOC styles is displayed. You can save time by choosing one of the built in TOC styles or you can click Insert Table of Contents... at the bottom of the menu to define your own TOC style.

Automatic Table 1 and Automatic Table 2 will insert an automatically generated TOC based on the headings already present in the document. If you choose Manual Table, however, a structured TOC template is inserted but you must fill in the contents manually.
You can specify a variety of attributes for your TOC, including the format and how many heading levels to show. It may be that you are only interested in adding an 'at a glance' table of contents; in this case you might elect to show only level 1 headings. Whenever you change a property, the print preview shows you how it will look before you actually insert the TOC.

Updating The Table Of Contents
What if you insert a table of contents and then change the document? If this happens you will need to update your TOC. Updating one of the built in TOC's is easy; click anywhere in the TOC and move your mouse up to the top left. Click on the Update Table... button and you can then choose whether to update only the page numbers or to update the whole TOC. The other button allows you to change the style of the table of contents or to remove it entirely.
Adding Entries To The TOC
To add an additional entry to the TOC, highlight the text you want to add and then click Add Text (still on the References tab). Using the drop down menu select what level the text should appear. Note that although you may have only selected a small portion of text, the whole paragraph will appear in the TOC. The new addition will not appear in the table of contents until you update it. For speed (and laziness!) click in the TOC and press F9. Select Update entire table.
Removing Entries From The Table Of Contents
You can just as easily remove the new entry by selecting it again, clicking Add Text > Do Not Show in Table of Contents, and again updating the TOC. When adding entries in this way, formatting changes may occur. If the text you've chosen to insert was styled using the normal style, the whole paragraph will be formatted using the heading paragraph style for the level you selected. If the paragraph was already styled, the style is retained and the TOC entry adopts the style of the level you selected.
By default, Word includes all headings in your table of contents (though you can specify what levels appear), but you can also indicate that other custom styles should appear in the TOC. Position the cursor where you want to insert the TOC and click References > Table of Contents > Table of Contents > Insert Table of Contents > Options. Select the custom style you want to add and indicate at what level the entry should appear in the TOC.

Marking Text To Appear In The Table Of Contents
You can also mark other text to appear in the TOC by creating a TC field. Unlike the method we saw earlier, doing this does not include the whole paragraph. Select the text to add and click Insert > Text > Quick Parts > Field and then select the TC field name. In the Text entry box type the text you want to see in the TOC. Click OK. Note that when you insert the table of contents you will have to turn off the styles option (see image above) and select Table entry fields in the TOC options dialogue box.

Related Links

How to create a table of contents by marking text in Word. From Microsoft Help and Support.
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