What kind of "new field"? A text field?
Yes, text, selected from a separated dropdown list.
As the custom calculation script of your text field enter something like this code:
event.value = this.getField("Dropdown1").valueAsString;
Adjust the field name to match the actual one.
How can I turn this automatic?
I had to click on the field to update the information...
It will work automatically, but if you want it to change the moment you make a selection go to the properties of the drop-down field and under the Options tab tick the box next to "Commit selected value immediately".