How do I make it so if specific option is chosen a textbox appears to fill in?

Hello andybose,

You can take advantage of our "Condition" feature to show / hide form fields based on the input / selection of user. 

Please take a look at the following demo form and see if this is what you want to achieve in your form:  http://form.jotformpro.com/form/40628747574970? Feel free to clone this form for a closer look. The following guide should help you in form cloning:  http://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL

Hope this helps.

Do get back to us if you have any questions.

Thank you!