When you create or edit a blog post, there's a panel on top of your tool bar where you can enter additional information for your post. Click to open it.
Enter a single word or a short phrase into the kicker field to classify your news thematically. This line will be visible in addition to the regular title within news overviews.
Please note: At this point, the kicker line is not shown within the news item itself, only in news overviews that come with the macros of the Enterprise News Bundle. Also, standard Confluence macros or macros of other plugins that show blog posts will not show this line.