HTTP is a stateless protocol, will not save the state of the communication between the client and server to save. This can handle a large number of things to ensure that the flexibility of the HTTP protocol.
But as web development, HTTP is stateless there are some problems, if the user logs on a website, even if the jump to other pages of this site, still need to maintain login state. In order to grasp the site is who sent the request, you need to save the user's login status. To achieve this, it introduced the Cookie, with Cookie, you can manage the state.
