Sorry for the late answer on this but I just saw it today.
Auto-responder codes can be added wherever you want to put them.
It does depend on what you are working with. Are you creating your own html page or are you using a wordpress platform.
If you are creating your own landing page you will put your code in the source section.
If you are using say Wordpress, you can put the code in a text widget.
Let me know if you need any further assist. I am pretty sure at this point in time you have already gained your answer to this question.