It's a long form, split into separate pages, but you don't have to fill in every box.
However, some boxes are required, and you cannot Continue to the next page or Submit the form without putting something in these boxes - even if it is just "NA". When you click "submit" the form should disappear, and be replaced with a "Thanks for registering" message.
You can step back and forward through the pages using the "Back" and "Continue" buttons.
If you cannot move to the next page, or the form does not vanish when you click Submit, check in case you have missed a required field, marked with a red asterisk.
If you have questions or problems, contact the Chief Marshal via the Contacts page on the rally web site http://mullrally.org/contacts/