The Class of 2020 application opens on August 1st. You can work on the application in Aug - Nov but you can’t submit it until November 1 - 30. https://www.universityofcalifornia.edu/news/admissions-application-open-aug-1
You can work on your Personal Insight Questions without the application being open. http://admission.universityofcalifornia.edu/how-to-apply/personal-questions/freshman/index.html
If you want to see the format of the rest of the application, look here: http://admission.universityofcalifornia.edu/counselors/files/apply-online-freshman-cal.pdf