AutoShip is a feature that will automatically send your book to print in 7 days once it has 60 pages in it. Your book will only head to AutoShip if you have opted into this feature in your Series Subscription and you have an available credit to go towards the AutoShip for your next book.
To turn AutoShip on, go to your Series Subscription and click into the Settings' Wheel in the upper right-hand corner of the page. Scroll to the bottom of the page and click "AutoShip". Click ON and "Save Changes". This prompt will look like this:
You now have AutoShip turned on for your Subscription.