Ordinarily, they are selected from the voting rolls and will be required to serve on juries periodically. In most jurisdictions, certain people can be exempted from or defer jury service, e.g., pregnant women, individuals who are ill, deaf or blind. Every state has rules that govern the conduct of a trial. Rules of evidence are designed to assure that only credible and reliable evidence is presented to the judge or jury. Hearsay evidence, for example, is not admissible.
Hearsay is an out of court statement that is being introduced to prove an element of a case.
Since the person who made the out of court statement is not in court and subject to cross-examination, hearsay evidence is not admissible. If a party attempts to introduce improper evidence, it will normally be objected to. The court will only direct a verdict where it is convinced that there are no disputed issues of fact for the jury to determine, and that a litigant is entitled to judgment as a matter of law. The jury will then retire to a jury room to deliberate until a verdict is reached. Ordinarily, the court will enter judgment based on the jurys verdict.