Okay, so imagine you and your friend Mitchell are playing a game. Mitchell breaks one of the rules of the game and you tell him that he's not supposed to do that. Mitchell gets really mad and hits you.
Now, hitting someone is never okay and it's against the law. So, the state (which is like a big group of people who help make sure everyone follows the rules and laws) gets involved. They bring Mitchell to court and accuse him of breaking the law by hitting you.
During the trial, the state says that Mitchell is guilty and presents evidence to prove it. Mitchell also has a chance to defend himself and prove that he didn't do anything wrong or that there was a good reason for hitting you (although there usually isn't a good reason to hit someone).
Ultimately, the judge or jury will decide what really happened and whether or not Mitchell is guilty. If he is found guilty, then he will face consequences, like having to pay a fine or going to jail, because he broke the law by hitting you.