Generally, cookies are small text files that some services use to save and store browsing data. For example, cookies can be used to save the products you have in your cart while shopping online or to keep you logged in on a site even if you close it and then come back after a while.
Cookies are stored on the browser while you are using it during the navigation: therefore, they refer to that browser, not to the person who is using it at that moment. If you want to know more about cookies you can watch this short video made by the Guarantor for the protection of personal data.