In order to make offers on cards or buy cards over time and have them kept in your online inventory until you are ready to, say, ship them all together in one batch, you must purchase COMC Credit and have registered for a COMC account, which is free to sign up for. When an item is bought outright with COMC Credit or via an offer, it is deposited directly into your COMC account (and therefore is not by default shipped anywhere).
Once any items are in your online inventory, they can each be marked as Ready to Ship by using the Actions button to the right of the card in your Inventory Manager. All items marked as Ready to Ship will be bundled and shipped together in the next shipment request that is placed using COMC Credit. Simply select the Buy Now instead of the "Add to Cart" button to purchase an item with COMC Credit
Additional details about COMC Credit can be found on our Add Credit page here.