Sometimes when you need required information in an application you need to ask a follow-up question that provides more information if the applicant answers primary question a certain way. That is when you can create dependent (parent & child) questions.
Here is an example: You need to ask the applicant an additional question because they answer Yes:
You can create a new custom application question that will only appear if the base question is answered a certain way. Scroll to the parent question that will have the child question (see red box below) and choose the answer that will trigger the follow-up question.
You can customize additional follow-up answers in the same manner any other custom question is set up.
Then when the applicant answers the question a certain way a new question will pop up. As with any field or question, you can choose whether or not the question is required.