Well, they maintain a database of people who are willing to share portions of their music collections with others. That is the end of Napster 's involvement. You must then contact the other person or persons and arrange to transfer the music over the Net. You may or may not be successful. When videotapes first came out, the courts decided that individuals may legally and properly, without payment to anyone, give copies of movies they have recorded off the air or purchased to other individuals.
Bad musicians get bad return.
Good musicians get lots. Furthermore, most music copyrights are owned by the recording companies, not the musicians. The necessity for copyright law was created by technology about two hundred years ago. This meant, that for the first 5800 years of civilization, itself based upon property rights, society saw no need for nor existence of intellectual property rights. As is certainly true, people reasoned, ALL creative ideas are presaged by a multiplicity of other related ideas.