PHP transparently supports HTTP cookies. Cookies are a mechanism
for storing data in the remote browser and thus tracking
or identifying return users. You can set cookies using the
setcookie() function. Cookies are part of the
HTTP header, so setcookie() must be called before
any output is sent to the browser. This is the same limitation that
header() has.
Any cookies sent to you from the client will automatically be
turned into a PHP variable just like GET and POST method data. If
you wish to assign multiple values to a single cookie, just add
[] to the cookie name. For more details see
the setcookie() function.