If you associate each level of a multilevel list with a unique paragraph
style, you can apply numbering by applying the appropriate paragraph style
to text. In fact, you are recommended to make use of style-based numbering.
It will be quite easy to make use of the heading styles, since there are
already built-in formats for those; see my previous message for the basics.
Note, however, that the general principles apply to any set of nine styles
that you want to attach to your list levels.
All aspects of numbering, including attaching paragraph styles, can be done
in the multilevel list dialog, which works pretty much the same as the
Customize Outline Numbered List dialog box of previous versions. You may
still find the article at
http://www.shaunakelly.com/word/numbering/OutlineNumbering.html useful.