Because the question was originally categorized as “business,” but seems to be inquiring about the civil justice system, it has been recategorized as “business law.”
There are multiple phases of a civil lawsuit, beginning with the filing of complaints by a plaintiff and possible filings of counter-suits by the defendant, and progressing through the pre-trial procedures, pleadings, motions, and so on. The discovery phase of a trial, whether civil or criminal, is the phase during which each party to the case presents information to the other that provides the basis for each side’s position. Information exchanged during discovery includes evidence and the list of witnesses that each side intends to have testify on his or her behalf.
One of the most important elements of a civil suit involves the taking of depositions from all parties involved regarding their observations, experiences or involvement in the matter that provides the basis for the suit. Parties to a suit will frequently “depose” each other as a way of forcing legally-enforced histories to be available prior to the initiation of the trial. As depositions are legally-binding documents – in other words, those being deposed are sworn under oath to testify truthfully in advance of the formal trial – they provide among the most important elements of a civil or criminal case and allow lawyers for each side to enter trial with sworn statements against which witnesses or parties to the suit can be questioned.
Another element of the discovery phase of a civil suit is what is known as “interrogatories,” which are written questions each side submits to the other that require written, truthful answers. Subpoenas are almost always issued in civil suits requiring individuals to appear at trial and be prepared to testify under oath as to his or her knowledge of matters relating to the suit. Subpoenas not only compel individuals to appear in court, they also provide a sense of moral protection to many witnesses who would rather be legally compelled to testify in a trial than do so voluntarily if their testimony is likely to prove injurious to a party to the case in a way that could adversely affect future relations (“I didn’t want to testify; they made me. They served me with a subpoena!”)
These are the main elements or “devices” in a civil suit, all of which occur prior to the initiation of a formal trial.