Cookies are used to store data on the browser, that will be reused at the next session.
They can contain everything: choices of language, colors, and sometimes password...

Read cookies in the server response and store them in a cookie jar.

$ curl  -c cookies.txt

Send a stored cookie, and update its value with the response

$ curl -b cookies.txt -c cookies.txt

Send a manually crafted cookie

$ curl -b 'code=1447'