Additional info input from radio buttons.

Additional info input from radio buttons.

Would someone please point me in the right direction?  I am looking to use a radio button with yes/no as the options.  When yes is selected I would like an additional text box to popup which allows for more information to be input.

Sorry if this is a simple question.  I am a newbie and have been searching through the help pages to no avail.

TIA

Bill