To begin working with applications in Facebook, you need to set up your account to work with the right tools. To do this, click Developers at the bottom of the screen, then Get Started. Next, click Add Facebook Developer Application to include the app in the list under your profile.
In your profile, under posted items, you'll see applications you've created using a third-party site, such as Popfly. Click one - in this case, ImageRotator - and you'll see various details of the application (including a URL that you'll need in step 5). Click Post to add the item to your profile so that you can start to work with it.
Next, select Developer under Applications on the lefthand side of the screen. The My Applications list on the right shows the apps you're currently working on - it should be empty. To get started on your app, click the Set Up New Application button at the top of the screen. This will take you to the New Application page.