Creative Commons licenses are made up of four core elements, which can be combined in different ways to make-up six standardised licenses.
These elements are:
Attribution - This element means that you must attribute the author of the work, and that attributon must comply with any conditions they require (such as linking back to a website). Attribution operates similarly to academic citations, in that it is about crediting the author of the work appropriately.
No derivative works - This means you can only use this work exactly as it currently is, and you can't alter it. For example: if it was attached to an image, you would be unable to edit the image using Photoshop.
Non-commerical - This means the work can only be used for non-commerical purposes, meaning that you are not permitted to make money off the use of it. For example, if a license with this element was attached to a piece of music, the music couldn't be used in a film which was going to be sold in stores.
These licenses vary from the most permissive (the 'Attribution' only license, which only requires that you attribute the content )
, to the most restrictive (the 'Attribution-Non-Commerical-No Derivatives' license which requires that you attribute the author or creator of the work, states that you are unable to make money off the work, and that you are not able to edit the work and have to use it verbatim or 'as is' ).