What is judgment (verb)? Judgment is an act of drawing conclusions from observations, usually to answer a question.
How do we judge? We use our judgement (noun) or intuition, which is built up over time with experience and pattern recognition. It is based on a set of judgment criteria, that we can call a rubric. This rubric is just like a rubric in school–it varies by assignment, subject, teacher, school, and person.
Why do we judge? To answer a question, gain knowledge, make a decision. Is it blue? Is it big? Is it dangerous? Do I have anything in common with this person? Is it better or worse than something else? Do I like this person? What should I do?