newbie : BIND VARIABLES

Hi all,
We have to use "bind variables" : What does bind variables means exactly ? relation ship with performance ? and how I can see if it used or not ? (V$SQLAREA,V$SQL,V$SESSION, ...)
I have also execute an ALTER SESSION SET AUTOTRACE TRACEONLY EXPLAN PLAN for .... and get 'HASH JOIN' : What does it mean HASH JOIN and HASH TABLES ?
Thanks Received on Sun Jun 16 2002 - 11:03:24 CDT