question about $_Session and $_Cookies

i have a question..

i'm still new to php...

may i know what the main purpose of using $_cookies in php
and also what the main purpose of using $_session?

how does $_cookies done the work?
how does $_session done the work?

any sample code so that i can learn more about it?

Use Google. Don't be lazy.

Tons of PHP Tutorials on Sessions and Cookies to be found out there, with just a little bit of research.

here:
let me google that for you PHP $_SESSION