This summary is not the rule. The rule text controls.
When a criminal trial ends, the judge has to give the jury instructions before they start deciding the case. These instructions explain the law that applies to the specific charges and facts in the trial.
The judge tells the jury that they get to decide both the facts and how the law applies to those facts when they figure out if someone is guilty or not guilty. However, the jury still has to follow the law exactly as the judge explains it to them. They can't make up their own version of what the law says.
The judge also makes clear that the jury alone decides how much weight to give each piece of evidence and whether witnesses are telling the truth. This means the jury has full control over judging the evidence in the case. The judge won't tell them which witnesses to believe or how important certain evidence is. That job belongs only to the jury.