Most people confuse copyright infringement with plagiarism. These are two different issues. One may do plagiarize without infringing copyright and vice versa. And one may do both. For example, one may plagiarize by presenting part of a work by Shakespeare as his/her own work! But since the works of Shakespeare are old and no longer in copyright (they are in public domain), there is no copyright infringement here. On the other hand, one can avoid plagiarism by properly citing and giving full credit to the original creator of the work, but infringe the copyright by using the work without getting permission from the copyright holder.
Plagiarism is the act of presenting someone else's work as one's own work. Plagiarism is not a criminal offense. It is an ethical issue. It is usually dealt with in schools and academia. It usually results in failing grades or expulsion from the school or losing credibility in the publishing world. Of course, the original creator of a work can sue the person who has plagiarized his/her work in court. But this would be dealt with in civil courts not criminal courts. It will be considered as intellectual property theft subject to monetary damage. In order to avoid plagiarism, it is required for everyone to properly cite every work used in creating the new works and give the proper credits to the creator of the original work.
Copyright infringement is the act of using someone else's work without permission. Copyright infringement is a criminal offense (felony) and it is dealt with in criminal courts. Fair use Guidelines permit limited lawful use of copyrighted materials. But if the use does not fall into fair use rules, it is considered infringement of the copyright, subject to prosecution.