Format templates are just the same as what you would enter in the header, footer, events list or location list format settings in the general EME settings.
But sometimes you want to define a different format for event or location listings, depending on the page you are. In this case you can use the old “format” option for the [eme_events] shortcode, but that is not a very flexible solution. So now you can just define templates and use them with the option template_id. E.g.:
You can also use templates for header and footers in the eme_events and eme_locations shortcodes, using the options template_id_header and template_id_footer. Also many other shortcodes support placeholders, see their explanation for that.