Manufacturing orders define the product you wish to build and the resources that are required to build it. They also designate when you wish to produce the product.
When it is time to actually produce the product, you then inform OpenERP of each of the products produced, and your manufacturing order changes to a status of Complete. In a typical workflow, your raw materials are moved out of the inventory and your finished product is added into your inventory.
After a product has been produced and has been put into the inventory, it can be packaged and delivered to the customer. Depending on the specific manufacturing environment, a product may not even sit in a physical inventory location at all, and instead may be shipped almost immediately to the customer. Meanwhile in another industry, you may have a product that is produced and then sits in a warehouse for months before delivery. Of course, it is always possible that...