Conditional event

This is for LiveCycle Designer 8.
 
I have a check Mark object. I need to set it up so that if the end user chose the box (X), the text field next to it becomes active so that text can be entered. I also need this text box to be required if the check box is selected. To better understand your response, please consider the check box name as ABC, and the Text Field as XYZ. Thank you