Hello,
If you purchased directly from NCH they should have sent you an email with the license registration code. if you purchased through a retail store you should have a yellow tag (paper) that has the Serial Number in it, this serial you must have activated at some point to receive the license registration code which is a code made of numbers and letters that you have to input into the program to complete registration. You must also have the version of the program that is compatible with your license installed to be able to use your registration code to complete registration.
If you are not sure you have the correct information I will suggest you contact NCH support for them to provide you the information you need to register and step by step instructions. You can create a support ticket for them through the link below:
https://www.nch.com.au/support/index.html