The Blog Sidebar
Your blog has a fully customizable sidebar. This sidebar include three sections / elements by default and these can be deleted just like any other element.
But you can easily add more content by dragging elements to the sidebar. There is a "Blog Sidebar" category that is meant to be used only with the sidebar, but you're welcome to use elements from any of the categories.
Here we see a sidebar that includes three of the default sidebar elements, a Flickr badge from the "Blog Sidebar" category of elements and a Blogroll (links to other blogs) that was created using a Title and a Paragraph element.