Cookies are small text files that websites place on the computers and mobile devices of people who visit those websites.
These text files allow a website to remember your device and how you interacted with the website, which is useful for a number of different purposes.
For example, cookies can be used to remember username and password information so that you don't have to re-enter all of your login information every time you visit a site you frequently log in to.
Other functions of cookies are to provide custom advertising to users based on searches and personal interests, as well as site performance cookies that enhance website use by remembering things such as custom video streaming or volume settings you have selected while using the website in the past.
Whenever you visit a website, the website sends a cookie to the device you're using to access the website. Your device automatically stores the cookie in a file that's located within your web browser.
When you revisit a site, the website will respond in a more personalized way, remembering your preferences, providing faster page load times and so forth.