Oh, right. I thought that you were talking about actually creating the button itself. Now I know what you meant by "html code"...
Glad the link helped.
A Book Blog Button is a small button that represents your blog. It usually has your blog name on it and an image that is similar to or a cut out of your banner. Other people use the button to put for example in their sidebar and link to your blog to show they are regular readers of your blog.
all you need to make a button is powerpoint and a pic....that's what I use.