It sounds like you would like to customize your blog, is that right? So, from the page you referenced above, Appearance > Custom Design, you can click on Fonts, Colors, or CSS tabs to modify the appearance of your blog. You can find more information about the Custom Design here: http://en.support.wordpress.com/custom-design/
Or you could let me know the specific task you'd like to accomplish and where you are running into issues with it, and I'll be glad to assist further.