Inserting

The break will be inserted at the insertion point
When you insert a new section the section formatting will be the same as that in the previous section.

Automatic Section Breaks

There are a few occasions when Word will insert a section break for you automatically.
1) If you create a two or more column layout from this point forward.

Page Setup - This Point Forward

If you want to change the Page Setup for a particular document do not use the "This Point Forward" option.
SS
Word will automatically insert a section break for you !!

Columns - Selected Text

(Format > Columns)
If you select "Selected Text" word will automatically insert section breaks for you.