You set the URL for your blog when you create it by filling in the ‘Blog Domain’ line on the ‘get a blog’ page. Choose carefully because the URL cannot be changed once it is set.
You can find the URL by logging into Classcaster and going to your Dashboard page and selecting the ‘My Blogs’ link on the left hand menu. Then check the ‘Primary Blog’ line for your blog’s URL. If you have more than one blog, use the drop down list to see the URL.