Judgment is the mental ability to understand something, form an opinion and reach a decision. You have great judgment of character, which is why your friends ask you to meet their significant others when things get serious.
A decision is a judgment, unless you let a coin toss decide for you. Use your judgment to determine how much salt to add, or the safest way home. In court, the judge's official decision is called the judgment, and if you condemn someone, even if you're not a judge, we say you've "passed judgment." If you need to explain many parts of the story before your innocence will be clear, ask your listener not to rush to judgment.