Ah, so there's a bit of confusion because you probably received a couple of emails. One was about "inviting you to contribute to Artful Jackrabbits" , which you need to accept to become an AUTHOR and create posts. You need to do this!
You probably also got another email about "subscribing" so that you get emails whenever other people post. (this part is optional).
Try searching your inbox for an email with subject: "You have been invited to contribute to Artful", and click the "Accept Invitation" button inside that email.
Once you do that, you should be able to log in at http://www.blogger.com, and then click on "Posts" and there's an orange "New Post" button. (You can also save drafts until you're ready to publish them.)