[PHP] multiple queries, one transaction

[mayo]

I have a site where I need to do multiple queries in sequence. 
 
 
I see there is a way to do consider all querys and to fail the entire
procedure if one query fails. It's a BEGIN and COMMIT statement.
 
mysql_query("BEGIN"); // starts the transaction
 
 
mysql_query("COMMIT"); // ends the transaction
 
I'm just not certain how it's used.
 
Thx, mayo