Once you complete checkout, you should be brought directly to a page to choose your password and then login. Your username is the email you used to purchase.
Otherwise you can access your purchase by going to the JVZoo customer portal at https://customer.jvzoo.com
Login, then find the highest level you purchased--if you purchased the main offer and 2 upgrades just go to highest upgrade--and click View Details button.
Scroll down until you see a green Access Your Purchase button and click that and it should bring you to the page to create your password and login.