[eluser]mddd[/eluser]
An Ajax response is just like any other CodeIgniter page. Use a model to gather the information, use a view (if necessary) to form the data for output.
If the output is JSON you can probably just return it from the controller without needing a view.
[eluser]Zion.b.y[/eluser]
if you know how to use ajax,
then it is very much the same in CI,
simply in the url (in the ajax call) use the code igniter struction of url's.