Website - is the top-level container for sites, shipping methods, payment methods, and more. To create completely separate sites that do not share cart, shipping methods, or other you must create separate websites.  A website contains at least one store.
Store - is contained by a website. In turn, a store contains at least one store view. Multiple stores can share cart, user sessions, payment gateways, and more, but they have separate catalog structures and Catalog price.
Store View - it change the way pages are presented, and are typically used to display a store with different layouts or languages. You can manage different currencies per store view.