When you create media for distribution on the web (such as a podcast) you have rights to control what others can do with your original work. Likewise, you are limited with what you can use from other people. This is where copyright and Creative Commons come in handy.
Copyright rules are great for protecting people's intellectual work. A great article helping to explain copyright can be found here.
Creative Commons is something that has recently developed and helps people to share their work and modify the work of others. Great explanation can be foundhere.