There are no widgets. Currently the slideshow will only display all photos attached to a post. Please see here for all the slideshow choices we have. Be sure to note those under “Related”. http://en.support.wordpress.com/slideshows/
As your are new to WordPress.com this is a link to a helpful tutorial prepared by Staff. And this is the link to the main page for all support documentation. The search box there provides results form both the support docs and from forum threads.