Set up your iCloud account
To use My Photo Stream, you must set up a free iCloud account. With an active iCloud account, you can set your Aperture library as the main repository for all your photo stream photos. You can also choose which photos you want to download from My Photo Stream into Aperture, as well as the specific photos in your Aperture library that you want to upload to My Photo Stream.
Note: You must have an Internet connection to set up an iCloud account.
Set up an iCloud account for the first time
In the Library inspector in Aperture, select iCloud.
Click the Use iCloud button, and click Continue in the dialog that appears.
In the iCloud pane of the System Preferences window, do one of the following:
Enter your Apple ID and password, and click Sign In.
Note: If you can’t remember your Apple ID and password, click the “Forgot password?” link, and follow the onscreen instructions.
Click Create an Apple ID, and follow the onscreen instructions.
Note: For more instructions on setting up an iCloud account, see Help Center.
You can now return to Aperture to begin working with My Photo Stream.