There are different kinds of crimes. Some are much more serious than others. Felony crimes are more serious than misdemeanor crimes and you could be locked up for a longer period of time. In some very serious cases, youth may have to go to adult court.
Some crimes can be either a misdemeanor or felony, depending on what happened. For example, if you get into a fistfight you could be charged with misdemeanor battery. But if you hurt someone badly in a fistfight, you could be charged with felony battery.