Here is the key difference.
Alibaba is a marketplace. They do not own the inventory of the merchandise sold. They put buyers and sellers together. Buyer and seller agree on terms online via their platform or offline.
Amazon’s main business is they own the inventory, and sell directly to the customer.
Both models have their Pros and Cons. Amazon has also turned into a very strong third party seller platform in recently years, but they still like to control a lot of the fulfilment.