populate a text field when selcting from a dropdown list


Can I please get some help here. I have a drop-down list on a form, when clicked on it, two headings Area and Area Name appear, underneath them there are values. when I select a value under Area, that value appears on the drop-down as a selected value, but when I select the value under Area Name, it does not appear on the drop-down.

I’m supposed to create a text field/ input field aside so that when I click on the value under Area, the value under Area name must be populated on the text field automatically for each and every value on Area that corresponds with the value under Area name.

Hope I explained well, not very good in explaining.