How can I add co-authors to a Blogspot/Blogger?

I searched all over Google for the answer, but couldn’t seem to find it. My friend and I decided to start a blog together (Where I would also post the “Badge” widget) It is a Google Blog, Blogspot, Blogger, whatever you want to call it. I know there is a co-author feature, but I can’t figure out how to do it. Any blogging experts out there who can help?