Setting Cookies

W
hen the site wants to send a cookie to the browser, it uses a Set-Cookie header like this: 
Set-Cookie: cs_mode=edit; Max-Age=86400; 
            expires=Thu, 12-Jul-2001 18:12:10 GMT; Path=/; secure;
            Domain=www.cs.uchicago.edu;
The first part, cs_mode=edit, gives the name and value of the cookie. The remaining pieces are instructions to the browser regarding when and where the cookie should be sent back to the server. In this case, the cookie will be sent back on every request to www.cs.uchicago.edu until Thursday, July 12.

See the Cookie RFC for more details on the mechanics of cookies.