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 .
Want more stuff in your sidebar? 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.
For example, you could create 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.
Want less stuff in your sidebar? Hover your mouse over the element you want to get rid of, then click the X that appears. Yes, you can even delete the default fields (like Author, Archive etc).
If you absolutely hate sidebars, you can turn it off completely. Go to Settings > Blog and toggle the Blog sidebar field to OFF. Once you click save and Publish, your sidebar will be gone and your blog posts will expand into the extra space.