A more thorough explanation:

Definition: Jury instructions are written instructions given to the jury by the judge to guide them during deliberation. They explain the basic procedure of the deliberation and the substance of the law on which their decision is based.

For example, in a criminal trial, the judge may instruct the jury that the defendant is presumed innocent until proven guilty beyond a reasonable doubt. The judge may also explain the elements of the crime the defendant is charged with and what the prosecution must prove to establish guilt.

Attorneys may propose instructions to the judge, but the judge makes the final decision about content and phrasing. The instructions should be brief, concise, relevant to the case, and understandable to the average juror. They should correctly state the law without misleading the jury or inviting unnecessary speculation.

If an attorney opposes the jury instruction, they must properly preserve their objection for appeal. If a judge notices a flaw in the instructions after they are issued, they must immediately correct them. Historically, most successful appeals were the result of errors in jury instructions that confused jurors.

To reduce errors, many jurisdictions use model, standard, or pattern instructions approved by a state court, bench committee, or bar association. These instructions are not binding, but they ease the process of drafting fair jury instructions and theoretically do not have errors.

Overall, jury instructions are important because they ensure that the jury understands the law and applies it correctly to the facts of the case.