Sometimes you’ll see ‘Just another WordPress.com site’ written at the top of a blog. This isn’t compulsory advertising, it’s something you can change and use to give visitors an idea of what your blog is all about. Getting it right is important, because it’s probably the second thing people will see when they visit your blog. If the blog title is the front door, then the tag line is the entrance foyer. A good tag line is also an important part of SEO (search engine optimisation): see Focus on Title Tags and URLs in this article.
To change the tag line go to your blog’s dashboard. On the left is a column of icons and the bottom one is Settings. Click on that, then General. Change the tag line or leave the box empty if you don’t want an entrance foyer, and be sure to click on Save Changes when you’ve finished.