PHP Cookies and session variables

I am confused with the cookie and session functions.
I am trying to write and read a persistant cookie. I want that when a user logs in the first time, to save their username to a cookie so that the next time they viist the site, I know who they are.
Also, I need to keep session variables with information just about the current session. I have been reading tutorials but I am still unsure of which functions are for cookies and which are for sessions.

Thanks

Ok, I think I have it now. Please tell me if I am wrong.
setcookie() is used for both sessions and persistent cookies. If you give it a date, it will persist. But, if you don't give it a date it will die when the browser closes????

ummmmm, i think thats correct. if you dont specify a date for a cookie then it will dissapear when the sessions ends :)