What you must show in a trial to prove your case is the burden of proof. It lies on the prosecution or the plaintiff.
According to Cornell Law School, the burden of proof is different for tort law and criminal law cases. In a criminal case, the prosecution must prove its case beyond a reasonable doubt.
Civil vs. criminal
The burden of proof for a civil case is different from a criminal case because there is not as high of a standard to prove. In a criminal case, the court must consider Constitutional rights for the accused, such as the presumption of innocence and right to a fair trial. The goal is to prove someone is guilty of an act. Such concerns are not applicable in a civil case where the aim is proving someone was likely negligent.
Civil case burden of proof
In tort law, you must prove your case by a preponderance of evidence. You must show there is over a 50% chance that what you claim is true. For example, you must show that it is most likely that a company was in the wrong and that led to your injuries or damages, but you do not have to remove all doubt that the company may not have been negligent.
Evidence of claim
You will provide a preponderance of evidence by offering things that back up your claim. For example, you may bring in an expert to testify on your behalf, or you could provide physical evidence showing the extent of the damage or the faulty product. Witnesses also can act as evidence if they saw firsthand what happened.