A warehouse describes a facility serving the purpose of storing goods. In ecommerce, warehouses are mainly used to keep items on stock to make sure the short delivery times needed can be fulfilled. Obviously, there are many other uses for warehouses outside of ecommerce. Just think of production warehouses with parts or warehouses to serve as a buffer between production and expedition. Whatever the use of a warehouse, they all follow the same principle of inbound-storage-outbound processes: stuff comes in, is stored, and goes out again.
Inbound processes are processes that have to get articles inside your warehouse. Think of incoming goods inspection, returned goods inspection, unpacking and (re)labeling. This process is very important because when something goes wrong here, you might have incorrect stock information and you might have to disappoint a customer. Also, when you have to "fix" any problem later in the warehouse process, it will be more costly in terms of money or time.
Storage processes are needed to get the articles in the right spot in your warehouse. The "right" spot can differ per warehouse and the industry you are in. It includes trivial things like putting ice in a freezer but also taking into consideration how fast a certain item will sell; you will want to put that on a convenient location. There are many ways of storing items, from simple racking to Automated Storage and Retrieval Systems (AS/RS). Many warehouses will use different technologies, based on the needs of the items they want to store.
Finally, outbound processes include the work needed to get items out of your warehouse. At the very least this includes order picking, but it can extend to order consolidation, packing, value-added-services and much more. The outbound processes are often done using paper lists but can be easily digitized to use bar code scanners or other means. There is a lot of technology available for streamlining outbound processes, each with their own advantages and disadvantages.