Click the "Add a form" link
Fill in all the form sections
When all the sections are filled in, make an order and pay for it (you won't need to pay for prepaid forms)
You'll get an email notifying you that the DS-160 was successfully filled in (provided there were no errors in the form data) within 24 hours after this
Visit the order status page and follow the instructions you'll find there
After you follow all the steps on the order status page (review the form and sign it) you'll get access to the DS-160 confirmation page