There is no warehouse of finished Macintosh computers, waiting to be pulled out and shipped to you. Each and every unit is built to an order in huge factory in the Far East, historically China.
In almost every case, the store has ONLY the floor samples on display, which can not be sold as new, and essentially NO units in stock, (except in very rare cases.)
Some stock units that are expected to be in high demand may have been ordered internally, and may be available for more rapid delivery to a wide area, such as any the Apple stores in a specific Metropolitan Area. Exactly where this Metropolitan Area stock is kept is unknown. Some are guessing that stock may be in the back room at the various stores in that same Metropolitan Area. So users MIGHT find that their high demand unit could be handed over today -- but that is quite RARE for computers -- more common for iPhones.
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The different 'states' that your order can transition through are described in this document, and are roughly:
Order Acknowledgement, followed by 'Processing' -- which is described above
'Preparing to ship' -- your unit has passed all testing, been packaged, and moved to the shipping area of the factory.
'Shipped' -- your items was handed to the international carrier and has left the factory
Next, your item is handed over to a local (in country) delivery agency for expedited delivery to you or to an Apple store. At this point, home delivery orders are generally sent an expected delivery date.
Pickup Notification -- its available at the store or at your door.
Unfortunately, Apple has been using slightly different terminology for these steps, so the actual wording may be different.
the process is described in this document as well:
Shipping & Pickup - Shopping Help - Apple