How to make blog to from two column to become three column (inculde one blog post and two `add page

<body> <center>Sorry you do not have frames enabled. Here is the link of the tutorial:<br> <a href="http://chuanling616.blogspot.com/2008/01/how-my-blog-change-to-three-column-of.html">http://chuanling616.blogspot.com/2008/01/how-my-blog-change-to-three-column-of.html</a></center> </body>