How to Create Drop Down List Actions?

hello,

i was wondering how to create such drop down list action in Adobe Livecycle that when i choose one List Item it shows certain text fields under to it.

ie.

im having one drop down list that is having 2 List Items 1st is Yes and 2nd is NO.

Now, if i want to show some text fields under to it when i choose Yes and hide some text fields when i choose No, what do i have to do?

also wanted to know that how to show text fields in popup box when i choose Yes.

thanks in advance!