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.
If you don't want the blog sidebar to appear on your blog page, you can turn it off. To do this, visit the Settings tab, then click the Blog section of the Settings tab, you will find an option there to toggle the Blog sidebar on or off using the available toggle button.