Trigger With .txt File Output

Hello,

This is my first SQL trigger. I trying to create a trigger that will capture update operations on multiple columns within the same table, and output the content of those updates to a .txt file, local on the server.

I have searched this forum, but cannot locate the syntax of this command. Would someone be so kind as to provide an outline of the syntax required to do this? ie;

CREATE TRIGGER [Table_Change] ON [dbo].[table1]
FOR UPDATE
AS
Update (column1, column2, column3)
etc, etc....

Many thanks to all who reply. If I have overlooked this information already posted here, please direct me to the proper location.

Cheers.