IF THEN combo box

In the creation of a Form, I need to add an if then statement to a combo box.

When an option in a combo box is selected, I need an additional label and combo box to appear.

For the THEN part of the statement what do I need to do to have the box appear? I want it to either be invisible or disabled unless the option in the combo box pertaining to it to be selected. Is this possible, or is there an easier way to do this?

Thanks