In any trial, two kinds of questions will have to be decided at various times. These are questions of law and questions of fact. The judge decides the questions of law. You decide the questions of fact. After you have decided the questions of fact, you will apply the law to the facts as directed by the judge at the end of the trial.
Questions of law involve the determination of what the law is.
Or they may involve questions of substantive law, which create, define and regulate the rights of parties. Quite simply, it's deciding what really happened in a case. Don't be surprised if the evidence given by both sides is conflicting or if the testimony given by one witness contradicts another. After all, if everyone was in agreement about what happened and what should be done about it, the dispute probably wouldn't be in court, and a jury probably wouldn't be needed. Your job is to listen to all the testimony, consider all the evidence, and decide what you think really happened.