You then specify mappings from Umlaut html sections to HTML divs on your page. Umlaut html sections are configured in Umlaut in the "partial_html_map" configuration param, which by default is set to the "bg_update_map" config params :divs key. To see the sections in a default Umlaut installation, see: environment.rb in svn, look for bg_update_map. The :divs key of the hash there is an array of hashes, each individual hash has a :div_id key that corresponds to the html_sections id in this api response. For Umlaut developers, the :partial key tells you what Rails partial is used to generate this section.
An example is best: