Good Advice, check the guide for a sample.
The NOC code preferance means, that which JOB is your FIRST priority, and then IF that is full (capped) IF your job matches the second (if any) OR you have worked in 2 jobs that are elligible for applying, which one would you want first and then second. example,
I am applying as a specialist that is 3111, BUT I can also apply as a medical doctor that is 3112. BUT my preference is 3111.
So I will write, In Application as well;
3111 - Specialist
3112 - Medical Doctor.