A family of Microsoft word processing software products for creating web, email, and print documents.
The TC (Table of Contents Entry) field is very useful, but it is not for creating a "manual" Table of Contents.
The Manual Table of Contents choice is to create a Table of Contents in which the user types the entire table. It just gives a format.
You may be thinking of the Custom Table of Contents, which does use the TOC field to grab things (including TC fields) from the document and create a Table of Contents. I find the manual TOC so unhelpful that I removed it from the gallery for adding a TOC on my system.
The TC field is used to create entries that are not necessarily outline level paragraphs or certain styles. The text need not appear anywhere in the document. It is a hidden field.
However, I think the best source on how to tweak a Table of Contents in Word is TOC Tips and Tricks by Suzanne Barnhill, MVP.
The part on TC fields is found at http://wordfaqs.ssbarnhill.com/TOCTips.htm#TCFields.
I like Deborah Savadra (the Legal Guru)'s pages and find them very useful. Here is a link to her blog page: https://legalofficeguru.com/blog/ She has a number of fine YouTube videos as well.