> I need to know where can i find the definition of all the keywords for Interbase 6, there are some

of them i don't know wich is its functionality......

You can download documentation e.g. from www.ibphoenix.com (download section).

> Something else, is there any keyword or function that make the operation contrary to EXTRACT??

InterBase has built-in conversion from string to date/time,
it understands several formats, e.g.
'2003-12-31'
You can construct the string by concatenating it's parts, like
datefield = yyyy || '-' || mm || '-' || dd;

Ivan