Templates allow you to export your database to a large variety of formats. It also allows you to customize to a great extent how the data is exported.
To export using templates, choose the "Export..." menu item, which can be found under the "File" menu. You can choose the template from the "File Format" popup button. You can either export the whole database, or just the references which you have selected.
BibDesk provides several default templates, for export to HTML, RSS, Rich Text (RTF, RTFD) and to windows Doc format.