1. When do I need my purchase code?
When you purchase the item from Codecanyon, you will get a file about license certification and purchase code at their download page. Purchase code is required when you install the script. You will be asked to enter the purchase code at the last step of the installation.
2. How does the purchase code work?
The basic license policy is one purchase code, on active installation. You can install the script in the same server with the same domain unlimited times. But once you change the domain or server, you need to reset the purchase code and install again. As per how to reset the purchase code, please read here.