InfoPath Dev

I have created an email form that I would like to have some property validation assigned but I am not sure how to make a text box required only if certain check boxes are checked.  If they aren't the text box does not need to be filled in.  This is the first time I have tried to do create an infopath form and have no idea what the capabilities are when it comes to email forms.  Any help would be appreciated.

I see you've attached your form, but you didn't mention which fields you're talking about.

I am sorry. I want the justification box to be required if one or more of the Alternate Options are checked. If the Preferred Option is checked the justification box does not need to be filled in.