You are most likely talking about the Macromedia Coldfusion MX Developer Certification. In order to becoem certified, you schedule the test - take it - and pass with enough right answers. How hard is it? I'd say it is fair. I'd recommend you have a reasonable understanding of the language and features of CF before trying to take it. You can find study guides online as well as other resources to help you pass the test.
www.macromedia.com