-One responsibility of an American citizen is to vote. Voting is a very important key in having a strong national government. It is also important to vote for your community because when you vote, your voting for a person who you think would be a good leader of something, like class president, mayor of your town, senators for your state, governor of your state (and other state offices,) and then the president and vice-president of the country. When you turn 18, you have the right to vote for federal officials, and your state officials. We sometimes take the freedoms and rights given to us for granted and don't know how lucky we have our equal laws compared to other countries, where there is not much equal power based on gender, religion, etc.
-Another responsibility we have is to voice your opinion. This could mean like if you wanted to change a law in your state, you could inform your state representatives about it to take it to Congress, you could also say what you're thinking, whatever the issue is, out loud in a peaceful matter. Or you could also voice your opinion by taking a bill to Congress through your representative, and if it's a good enough bill, it could be passed and made into a new law.
-One more responsibility of a U.S. citizen is to accept responsibilities for your actions. If a person commits a crime, they would need to take in their punishment as a responsible person rather than run from it or deny it. Sometimes a person really doesn't want the crime to be on their record, so they have to wait awhile and pay a certain amount of money to get it removed.