After doing the initial conversion from MS Word using Mobipocket Creator, click on "Guide" in the menu on the left of the MPC window.
If there are no guide items listed with type "TOC", click on the "New Guide Item" button.
In the "Type" box, select "toc" from the drop-down list - the "Title" box should then be autofilled with "Table of Contents".
Now click on the "Browse" button next to the "Filename" box. You want to find the HTML file that MPC has created for this e-book. Select that and click "Open" so the name of that HTML file is now displayed in the "Filename" box.
Click inside that box and move the cursor to the end of that filename (after the "L" of "HTML").
Now type a hash (#) followed by the name of the bookmark you inserted at the start of the table of contents.
And finally click on the "Create" or "Update" button to add that guide item, and then rebuild the ebook.
Now when you view it using Kindle Previewer or on an actual Kindle, the "Table of Contents" item in the "Go To..." menu should be active, and should take you to the table of contents you created.