To speak about law and legal terms, you need the appropriate vocabulary.
Complaint - when someone says that something is wrong or not satisfactory;
Plaintiff - someone who takes legal action against someone else in a court of law;
Court - the place where a judge decides whether someone is guilty of a crime;
Defendant - the person in a court who is accused of a crime;
Paralegal - someone who ​works in a ​law ​company, or a company's ​legal ​department, and has some ​legal ​training, but does not have all the ​qualifications to be a ​lawyer;
Attorney - a lawyer;
Jury - a group of people in a court of law who decide if someone is guilty or not;
Prosecutor - a legal official who accuses someone of committing a crime, especially in a law court;
Witness - a person who sees an event happening, especially a crime or an accident;
Verdict - a decision in a court of law saying if someone is guilty or not;

Judge - someone who controls a trial in court, decides how criminals should be punished, and makes decisions about legal things;
Proof - a fact or a piece of information that shows something exists or is true;
Appeal - a request to a court of law to change a previous legal decision.
The suspect appeared in court charged with robbery.
The judge ruled that they had acted correctly.
She showed us her passport as proof of her identity.
He won his appeal against his jail sentence.