The add to cart forms are just like any other html form. You can add in whatever inputs you would like. If you are trying to get some info from this page to the confirm page you will need to store it in a session variable. To do that go to Server Behaviors > eCart > General > Set Session Value. For the trigger use the lightning bolt to select the add to cart button, then give it a name and for the value use the lightning bolt to select the text area.
Once you have done this you should be able to display this value anywhere on the site by going to the bindings panel and in the session variables find your new var and drag it onto the page.