The judge will advise the jury that it is the sole judge of the facts and of the credibility (believability) of witnesses. He or she will note that the jurors are to base their conclusions on the evidence as presented in the trial, and that the opening and closing arguments of the lawyers are not evidence. Sometimes judges will explain what basic facts are in dispute, and what facts do not matter to the case.
The judge will point out that his or her instructions contain the interpretation of the relevant laws that govern the case, and that jurors are required to adhere to these laws in making their decision, regardless of what the jurors believe the law is or ought to be. In short, the jurors determine the facts and reach a verdict, within the guidelines of the law as determined by the judge.