Creative Commons gives authors a way to share their work for free while retaining ownership. They offer six different licenses, and all a creator needs to do is attach one to his or her work. CC licensed materials are great for music, photos, sound effects, and more. Using them correctly (i.e. following the rules of the licenses), they also give a way to avoid most copyright problems.
Give credit when using Creative Commons material. The creators are letting you use their material for free, so it's the least you could do.
They also have a great Search Page to help you find openly-licensed material.
This license lets others distribute, remix, tweak, and build upon your work, even commercially, as long as they credit you for the original creation. This is the most accommodating of licenses offered. Recommended for maximum dissemination and use of licensed materials.
This license lets others remix, tweak, and build upon your work even for commercial purposes, as long as they credit you and license their new creations under the identical terms. This license is often compared to “copyleft” free and open source software licenses. All new works based on yours will carry the same license, so any derivatives will also allow commercial use. This is the license used by Wikipedia, and is recommended for materials that would benefit from incorporating content from Wikipedia and similarly licensed projects.
This license is the most restrictive of our six main licenses, only allowing others to download your works and share them with others as long as they credit you, but they can’t change them in any way or use them commercially.