A criminal case is a lawsuit against a person for a crime committed by that person. The prosecutor, often a district attorney or city attorney, files the case on behalf of the state or local government (in contrast to civil cases filed by private parties).
Unlike civil claims in which witnesses testify and evidence is presented, criminal cases require prosecutors to prove the defendant committed the crime beyond a reasonable doubt. This is an extremely difficult standard to meet.
When someone is arrested on suspicion of a crime they are given a chance to have a judge or magistrate review the charges against them. This hearing is called an arraignment. The judge reviews the charges, advises the accused of their rights and sets bail. Bail is money or property that the accused must give to the court in order to be released from jail during the case. During this time the accused is also allowed to retain a lawyer if they wish.
After the arraignment there are a series of pretrial hearings that determine whether the case will go to trial or be resolved with a plea. During these hearings a defendant may be allowed to have limited discovery proceedings (information and documents related to the case). They will also be able to challenge the admissibility of any evidence at trial that the government is using to convict them.
The last stage of a criminal case is when the jury decides whether or not the defendant is guilty. During the deliberation process the jury will discuss the case, and the judge will give them detailed instructions about the crimes charged. If the jury finds that the defendant is guilty, they will be sentenced.