There’s a lot of media out there, but it doesn’t mean you can use it for commercial purposes or download, build upon, adapt and redistribute. I know your stirring inside because you wanted to use your new favorite song in a video that your going to make. Or you found some great footage for a news piece you want to do. In here you can use it if you get permission, last semester a student contacted the invisible children foundation and got permission to footage from the Kony 2012 youtube video. If you want to use footage or music in here that’s not yours you’ll have to do the same. Fortunately there’s sites out there that hold a databases of content that you can use. You’ll need to keep track of your sources in the process. Here’s a few CreativeCommonssearch, Freesound.org, and Internetarchive.org. I’m sure there’s more but you’ll have to do a search for royalty free content to find it. You can also use garage band to make your own soundtrack, with all the sound effects and instruments this program works great.
This video explains in greater detail what exactly copyright means.