Cookies are files, often encrypted, which are stored on your browser. They are created for a limited period when a user's browser loads a specific website: the website sends information to the browser, which creates a text file. Each time the user returns to the same website, the browser retrieves this file and sends it to the website server.
The information stored by cookies includes the pages you have visited, the type of browser you use, your IP address and even information you have entered on a website so that you do not have to enter it again.
There may be different types of cookies, depending on their purpose:
Cookies may be session specific, only being stored on your browser during your browsing session, i.e. until you leave the website or the app, and deleted afterwards.
Some of them may also be persistent: they remain on your browser after the session has ended (unless you specifically delete them)