Can I use a VB script so that a user enters a date in field one and field two auto fills with a date exactly 30 days out from that date?

You can accomplish this using this script:
This assumes the field into which the date is entered is named dateOne and the date is entered in this format: mm/dd/yyyy.  The script will fail if the user doesn't enter the date in the mm/dd/yyyy format exactly.  For example, entering 9/1/2016 or 09/01/16 will not work, but 09/01/2016 will work.