Creators can allow their work to be reproduced, remixed, and used without permission by applying Creative Common licenses to them.
The copyright owner has the exclusive rights to reproduce the copyrighted work in any form.
The work has a separate copyright from the item (score, CD, etc.). So a symphony could be in the public domain, but if a new edition of the score was published last year, it will have its own copyright
Most performances of copyrighted works require a license with the exception of "face-to-face" teaching
Where a copy is allowed under fair use, you can make one copy of sheet music per student. When copying under the fair use exemption, the copier should be sure the copyright notice always appears on the copies. Additionally, be sure the copy is attributed to the author.