A hallmark of the American legal system is the principle that there should be as few surprises as possible in the course of a lawsuit. Since the late 1940's, the federal court system has required disclosure of all relevant facts and documents to the other side prior to trial, and virtually every state has followed its lead. That disclosure is accomplished through a methodical process called "discovery." Discovery takes three basic forms: written discovery, document production and depositions.
Interrogatories are questions requiring your version of the facts and of your claims. They can be pre-printed "form" interrogatories, or specific questions asked just for your case called "special" interrogatories. Questions can range from the broad ("What happened on April 26, 2004?") to the specific ("Is it your position that the defendant was wearing sunglasses at 2:30 p.m. on April 26, 2004?"). If the questions asked are not fair questions or are difficult to understand, your attorney will help you decide what you should object to.
Requests for admission are not often used, but can be a very powerful tool. They ask a party to admit or deny certain facts pertaining to the case, and they carry with them penalties for not answering, for answering falsely, or even answering late.
Document production is fairly self-explanatory. Any party has a right to see most documents that even arguably relate to a case. Particularly in more complex medical malpractice or product defect cases, the documents involved can be voluminous. Increasingly, courts are allowing access to computer files as part of document discovery. In cases where enough is at stake to justify it, courts have even allowed litigants to reconstruct deleted files (like e-mail), although that practice has not yet become common.
Depositions are sworn statements, when a person will answer questions from an attorney, and a court reporter will make a transcript of all that is said. Depositions can range in length from an hour to a week or more. Although all attorneys have their own strategies for depositions, there are basically three reasons to do them: to lock people into their stories, to see what the other side has, and to do a "practice trial," that is, to see how a witness will appear and conduct themselves before a judge or jury.
Your attorney will tell you what he or she wants from you if you are deposed, but there are two general things to remember. First, never guess. The purpose of a deposition is to give facts, not to speculate as to what might have happened. Even if it makes you self-conscious to say it, sometimes "I don't know" is the right answer. Second, it is human nature to want to explain things so that your listener understands, but you should resist the impulse. It is your opponent's job to get the answers. It is your job to answer only the question asked, not to offer additional information.