What are cookies?
Cookies are short text files generated by a web server and stored on your computer via browser. When you return to the same site later, the browser sends the saved cookie back and the server gets all the information previously saved from you.
Principle of cookies allows to distinguish individual users and store specific data about them. E.g. thanks to the cookie, a server knows what language settings you have chosen during your last visit or what login name/details it should pre-fill into the forms (server remembers it from the previous visit). Therefore cookies make personification easier.