A lawsuit is a civil action brought by one party (the plaintiff) against another party or parties (the defendants) in a court of law or equity. It is a claim for money damages or other relief.

To file a lawsuit, the plaintiff must first gather facts that support their claims and perform legal research to identify the applicable laws. Then, they must draft a complaint that (1) meets all federal, state, and local rules for filing; (2) is concise and plain; (3) includes separate counts for each legal claim; (4) properly alleges subject matter jurisdiction, personal jurisdiction, and venue; and (5) cites to relevant statutes and cases that support these allegations.

After the complaint is filed, the plaintiff must serve it on the defendants. Usually, this means having someone hand-deliver it to them or hiring a process server to do so. Once the defendant receives it, they have an opportunity to submit their response to the claims made in the lawsuit and supporting documentation.

If the plaintiff successfully proves every element of their case, they win the lawsuit. The court will award them damages which usually mean the defendant must pay a sum of compensation to make them whole and may also order the defendant to do or not do certain things called equitable relief.

The plaintiff can also add new claims to the complaint after it has been filed as long as the statute of limitations has not expired. However, it is important to be very careful when adding new claims or changing old ones as some courts have specific rules about how this must be done.