How I can create Triggers?

A database trigger is procedural code that is automatically executed in response to certain events on a particular table in a database.

for example you can create a trigger to do not accept any phone format in the phone colmun but xxx-xxxx-xx-xxxx for example when the user inserts a different format the trigger prevent from saving that to the data base

example:

CREATE TRIGGER name ON table
FOR INSERT
AS
--put instructions here
GO
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