A trigger is a database object that is attached to a table. In many aspects it is similar to a stored procedure. As a matter of fact, triggers are often referred to as a "special kind of stored procedure." The main difference between a trigger and a stored procedure is that the former is attached to a table and is only fired when an INSERT, UPDATE or DELETE occurs. You specify the modification action(s) that fire the trigger when it is created.
The following shows how to create a trigger that displays the current system time when a row is inserted into the table to which it is attached.
SET NOCOUNT ON
CREATE TABLE Source (Sou_ID int IDENTITY, Sou_Desc varchar(10))
CREATE TRIGGER tr_Source_INSERT
INSERT Source (Sou_Desc) VALUES ('Test 1')
-- Results --
Apr 28 2001 9:56AM