Okay kiddo, so there was this guy named Matheson and he did something that the government thought was against the law. The government thought he had something bad that he wasn't supposed to have. So they took him to court to see if he really did it.
In court, the government showed evidence that they found in Matheson's house that they said proved he did something wrong. Matheson's lawyer argued that the evidence wasn't enough to prove that he did it.
The judge listened to both sides and decided that the evidence was good enough to prove that Matheson really did do something wrong. So Matheson was found guilty and had to face the consequences for breaking the rules.
And that's what happened in United States v. Matheson. Does that make sense, kiddo?