Make Some Noise
Have you ever messed up a play because someone yelled at the exact moment you were trying to throw or catch a ball? The same thing can happen to a visiting NFL team when the fans cheer very loudly. The term "home-field advantage" refers to the fact that most teams play better in their home stadium. They have their loyal fans in the stands and having the crowd on your side is a huge advantage.
If the crowd is making a lot of noise, then it can cause the other team to make mistakes. If an offensive lineman can't hear the quarterback because the crowd is so loud, that lineman may false start and his team would get a penalty. If the team can't hear what play is being called, they may think they are supposed to run left when they need to run right.
Not all noise can be used to help a team, however. Artificial noise is something that can hurt your team if it is too loud. But that kind of noise isn't caused by psyched fans. Artificial noise is caused by things like loud speakers. If a stadium is playing loud music when the away team is trying to run a play, then the referees might give the home team a 5-yard penalty for deliberately using something to distract the visiting team.
The lesson for you, as a fan, is to remember to cheer loudly for your team the next time you go to a game because it could help them win the game!