@Yogaraj congratulations on passing the multiple-choice!
When you purchase the assignment,
you should have only one thing to buy there. One price should cover both the submission and the essay.
If this was the page to which you were directed
http://education.oracle.com/pls/web_prod-plq-dad/db_pages.getpage?page_id=609&get_params=dc:D85846,clang:EN, then this is where you need to purchase the voucher. Click-to-expand the "View Details" button.
BTW, please be aware of the course requirement. This was not always there, but as of the last couple (?) of years, to get an OCMJEA you had to register for a mandatory course. The course could be the one specific to this exam, but does not have to be. If there is some
Java technology you need to know more about, this is your big chance. Only approved courses from their list will do. Also, it cannot be some CD course. They allow you to satisfy the requirement with either a sit-in class, or with an Oracle "Training on Demand" course. These cost $$. You should be aware of that.