A more thorough explanation:

Interrogatories are written questions that one party sends to another as part of the discovery process in a legal case. The purpose of interrogatories is to gather information that will be used in trial.

Attorneys can ask any question that is relevant to the case and not privileged. This means that they can ask about facts or how the law applies to the facts, but they cannot ask purely legal questions. For example, they can ask about specific statements made by a plaintiff, but they cannot ask why a statute does not violate the constitution.

Interrogatories must be responded to by the party being asked the questions within 30 days. The responding party must fully answer each question, but they can object to the questions if they believe they are not relevant or privileged. If a party refuses to respond to an interrogatory, the other party can compel them to respond.

For example, in a case where a plaintiff is suing a union for violating their rights, the plaintiff's attorney might send interrogatories asking for specific examples of the union's actions that violated their rights. The union's attorney would then have to respond within 30 days with a full answer to each question.