how to set conditions based on an answer to a question?

Well, it depends on the type of action you want to use. You can access the conditions wizard by clicking on Conditions icon.

You can choose the option based on your requirement that can be to hide/show one or some fields, changing sections/pages, send email, perform calculations, etc.

The conditions wizard is easy to use since it displays the field labels so that you can identify the fields to set the conditions.

Please refer to the following guide that can assist you in this regard.

http://www.jotform.com/help/57-Smart-Forms-Using-Conditional-Logic 

Hope this information helps. Let us know if you need further assistance.

Thanks!