There are many specific differences between the juvenile justice system and the adult system. These differences can vary from state to state. In general, though, we can say that there are two main types of differences. First, the adult system is more legalistic. Second, the juvenile system is more oriented towards helping and rehabilitating the offender than the adult system is.
Of course, both systems have some similarities. Both are meant, to some degree, to determine when an accused person is guilty and, if they are, to mete out some sort of punishment. Both are part of the US legal system and therefore both protect the accused’s important rights.
From there, though, the two systems are very different. The adult system is more legalistic. It is focused on following rules precisely. It has more rules that are meant to protect the rights of the accused. Adults are always tried by juries whereas juvenile cases are “adjudicated” by judges. The rules about admissible evidence are generally stricter in the adult system. In short, the adult system is based on following rules whereas the juvenile system is focused more on finding out what has happened.
Second, the adult system is focused on punishment while the juvenile system is focused on rehabilitation. Juveniles are generally treated much more leniently when they are found to have committed an offense. The idea is that they are younger and more able to change their ways.
These are the major similarities and differences between the two systems.