Highlight the word you want to link.
Right-mouse click and select Hyperlink.
Click Place in this Document.
Locate the heading to which you want to link.
Click OK.

This make an assumption that you are using Heading Styles for your section
topics.  If you aren't using Heading Styles, you can insert a Bookmark at the
location to which you want to link, then follow the same steps above but
locate the Bookmark instead of the heading.

Hope this helps,

Gilley