The newly introduced Bueno theme includes a unique widget: “Bueno Featured Posts”. Activating this widget allows you to showcase some posts in the sidebar. (You can add the widget to one of the footer cells instead of the sidebar, but that defeats the purpose of showcasing.)
You can title the widget any way you like; if you don’t type anything in the title box, the title in the sidebar will be “Featured Posts”.
Dropdown 1 (“Show posts tagged with:”)
If you don’t select anything, the widget will display your latest five posts.
If you select a tag, the widget will display the latest five posts tagged with that tag.
Important: the tag has to be a single word or it won’t work. [Update: problem fixed.]
Dropdown 2 (“Show content as:”)
If you select “Full content”, the widget will display complete posts. Definitely not recommended if the posts are long and/or if they include images or any other object wider than the sidebar.
If you select “Excerpts”, the sidebar will display the beginning of each showcased post. It can also display alternative custom-made excerpts or summaries, if you write those in the Excerpt module of the post editor (see here for more). If you see no Excerpt module on the post editor screen, click “Screen Options” (top right) to activate it.
The showcased posts can be accompanied by small thumbnails, as shown in the official screenshot of the theme reproduced here.
The thumbnails will automatically show up if you set a featured image to each post (or to each post tagged with the selected tag). For instructions on how to set featured images, see the relevant Support doc. Again, if you don’t see the Featured Image module on the post editor screen, click “Screen Options” to activate it.
If you set featured images, the thumbnails will show up no matter if you select Full Content or Excerpts in the widget dropdown. But in my opinion the effect is better if you select the Excerpts option (as shown in the screenshot); in fact, thumbnails or no thumbnails I don’t see any point at all in displaying full posts in the sidebar.
Featured images show up at the beginning of each post as well, on the main posts page and on archive pages (but not when viewing a single complete post); maximum dimensions 490×200 pixels (cropped if larger).
Note: The general look of the theme is customizable. You can change the background color or add a background image; you can also add a header image (will show up below the title and top navigation).
You can (must?) also change the horrible header font via Typekit; see here.