A cookie is information stored in smartphone or PC from the website you are viewing. There are various contents such as the data and time of visiting the site, the number of visits, etc are recorded there.
So why does the website need to store information?
Thanks to cookies to be able to see the website comfortably. For example, if you access a site once logged in by entering ID and password, such as Facebook or Twitter, after a while, you can go in without having to enter ID and password. This is thanks to the cookie where the login information is stored.
Or, while you are shopping at a shopping site, you log out with the item in the cart. After a while, if you access the same shopping site again, the items in the cart will not disappear and remain firmly. This is thanks to the cookie which stored the cart information.
In this way, cookie are extremely helpful in making the access and operation of the Web convenient, and enabling the provision of various services. Actually, if you do not enable cookies, inconvenience arises that websites are not displayed properly or you can not shop. Many of internet banking can not be used unless cookies are enabled.
Also, with cookies, websites can learn shopping history, user interests and topics, so they are also heavily used in corporate marketing analysis.