With a Musician Plus or Label plan, you can pre-sell your releases in iTunes, Amazon, and Google Play.
You'll need to set a release date to at least 5 days in the future (Musician Plus or Label plan required). After you have chosen your release date, you can select whether or not you want to enable iTunes pre-order. Click 'Yes', and then enter the pre-order start date.
That's it! Continue uploading as usual, and your pre-sale request will be sent to iTunes, Amazon, and Google Play when you're finished.
Pre-sale is not available in other stores at this time.