In civil law, a lawsuit is an action brought by one person against another. The person bringing the lawsuit, called the plaintiff, claims to have suffered some sort of damage by the other party, called the defendant. A lawsuit is filed with the goal of receiving some sort of remedy for the damage; this could be in the form of monetary compensation, an injunction to compel or prevent an action, or the enforcement of a right. In the US, you can file a lawsuit by writing and filing a legal document, called a complaint, that outlines the reasons for the suit.
Although it is acceptable for any citizen to file a lawsuit without the legal assistance of a lawyer, it is advisable to allow the lawyer to act as an intermediary between you, the court, and the person or party you wish to sue. It is important to file a lawsuit in a timely manner, due to a mandated time frame called a statute of limitations. A statute of limitations is essentially a time limit within which you are allowed to file a lawsuit in court. Note that the statute of limitations varies depends on the area in which you reside and the type of case you want to bring.
The first step in formally declaring your intent to file a lawsuit is to file a complaint. Before this complaint is filed, however, your lawyer, if you have chosen to hire one, will perform an investigation to decide if it necessary and just to file the suit. If the lawyer finds your claims to be warranted, he or she files a complaint at the proper court. When your lawyer who files the complaint, you are the plaintiff, and the person or party you are suing is the defendant.
The filed complaint details why you believe the defendant is at fault for a personal injury or damages either you or your property have sustained. Once your lawyer has filed the complaint, the court clerk drafts a summons, which means the lawsuit is legitimate, and the process now officially begins. The complaint and summons are then "served on" or delivered to the defendant. Once the defendant has been contacted and has been made aware of the charges brought against him or her, he or she is required to respond within the allotted amount of time dictated by the court.