Becoming 18 is a huge turning point in your life. As an 18-year-old, you will have many more rights---and also more responsibilities. If you are aware of these rights and responsibilities, you will be better prepared to face the future with confidence and be able to have fun without getting in trouble.
Working and Buying
As an 18-year-old, you can work without special rules or your parents' permission. You can rent an apartment and buy property (although you can't rent a car). You can get a driver's license that has no restrictions. According to the California Bar, "You can now sign legal contracts, open bank accounts and apply for credit cards on your own." This also means that you, not your parents, are responsible for paying your bills and meeting your obligations.
Alcohol, Tobacco and Drugs
Now that you are 18, you can legally smoke (although it is an unhealthy habit). It is illegal for you to give tobacco to an underage person. Now that you're 18, if you use illegal drugs the consequences may be more severe that when you were a juvenile and law enforcement might have cut you some slack. Depending on your school's rules, you could get in trouble there too, if you use illegal drugs or drink.
Sex and Marriage
It is now legal for you to have consensual sex with another person over 18. It is illegal for you to have sex with a person who is under 18 unless he or she is your husband or wife. It is still illegal even if that person is your girlfriend or boyfriend and he or she consented. The exact laws vary from state to state. You can also get married now without your parents' permission.
Criminal and Civil Law
Now that you are 18, you can sue someone in court. This also means that you can be sued. You can sue or be sued under civil law for something that is not a crime. If you do commit a crime, you won't be able to get away with it or go to juvenile hall. If charged with a crime, you have the right to a lawyer and you will be provided with a free, court-appointed lawyer if you can't afford one on your own.
Voting and Jury Duty
Now that you are 18, you can vote. You aren't required to vote, but if you want to vote, make sure to register before the election. You can also serve on a jury, if you are a US citizen and understand English. You must show up for jury duty (although once you are there, you might be excused), and your employer must give you time off for jury duty. If you are male, you must register for the Selective Service.