Cookies are small text files that websites place on your device when you visit them. They're basically tiny memory aids that help the site remember things about your visit.
When you return, these files tell us whether you've been here before and what preferences you had. It's similar to a shopkeeper recognizing a regular customer and remembering how they like their coffee.
Some cookies disappear when you close your browser. Others stick around longer to remember you next time. We use both types depending on what makes sense for the task at hand.