A family of Microsoft word processing software products for creating web, email, and print documents.
Pesach has explained how to do this with an automatic border. You can also apply borders manually, using the button in the Paragraph group on the Home tab. Click the button beside the border button (ignoring whatever sort of border it's currently displaying as the default) and choose Borders and Shading... from the menu to open the Borders dialog.
In addition to the various types of borders you can add, note the Horizontal Line button in the lower left corner. This allows you to insert a graphic element (prepare to be patient, as the preview sometimes takes a moment to populate). The "lines" displayed are all the clip art pictures that include the keyword "dividers." If you have a specific design in mind, you can check the box for "Include content from Office Online" and search. My search for "vine leaf" included a lot of graphics that are not dividers but some that would make acceptable ones.