What it is
Creative Commons licensing provides the public to use material with various levels of restrictions. It can be confusing to someone new to the concept of sharing information freely, so I found an info graphic that explains what each of the different licenses mean, as shown below:
Where to Find It
There are a number of sites in which to search, including Google and Flickr to name a few. This search engine will provide you media which you can use under the above stated licenses, enabling you to safely add photos or videos to your blog (for example) without needing to worry about copyright infringement. Just be sure to properly source your work to give credit, where credit is due!