After you  log in, click "my blog" at the top left corner, then click "Post new blog entry".  Post a blog entry is like sending an email: all you need is a title and a body of text, and then click "Submit" at the bottom of the page.

The rest is optional.  For example, you have options of adding tags, making hyperlinks, and adding images.  You have several ways to cite articles in journals.  You can also attach a file with you blog entry by clicking "File attachments" beneath the posting window. Learn more about what happens after you post a blog entry.