To open content in a lightbox, you can simply add the content you want to display to the action content of your marker or region entry.

This content can contain HTML. If you want to edit the content with the rich text editor, like the screenshot above shows, go to the settings page of the plugin and in the ‘Editing’ tab, in the ‘Action Content Field Type’ set it to WP Rich Text editor.

Once you have the content in the marker/region, make sure you set the click action to ‘open content in lightbox’, either the default settings of the custom options for your entry.