So... From SSMS, press the F1 key to get into Books Online. Then search for CREATE TRIGGER and start reading. I'm not being sarcastic here. If it's truly your first time, take the opportunity to teach yourself all about triggers so you won't have to ask such questions in the future. To really do it right, create a test database and some tables to practice writting triggers on so you can actually see what they do.

Triggers can be quite the tripping point in code and if you don't have a very firm grasp on what they actually do and how they work and how to use them, you're going to make some really huge and embarassing mistakes.