Creative Commons is a non-profit organization which created licenses that help you easily license your works to the specifications you want. These licenses tell users what they can do with the material they want to use. These licenses are useful for BOTH the creator AND the user (or re-user)! Creative Commons is also a place to search for content you can reuse (be sure to attribute the creator when reusing!).
There are six types of licenses found in Creative Commons and each of them have different restrictions to limit a source's usage.
1. CC BY
This license is the least restrictive of them all. This one specifies that to use the work, the creator must be credited. This is a restriction that every license here requires.
2. CC BY-SA
This license adds a restriction labelled SA. This restriction specifies that any works created adapting the source must also be given a CC BY-SA license.
3. CC BY-NC
This license adds a restriction labelled NC. NC means that if your work uses this work, it can not be for commercial use. No money can be made from the work derived from this source.
4. CC BY-NC-SA
This license uses every restriction discussed above. You must give credit to the creator, need to give your work this same license and can not earn any money from this work.
5. CC BY-ND
This license adds a new restriction labelled ND. ND works can not be used to derive new works and can only be distributed in its original form. This license allows for commercial use.
6. CC BY-NC-ND
This final license combines two of the earlier restrictions. This pair means that the work must not be altered or adapted and can not be used for commercial gain. It means you can share the source as long as you give credit, but you must show it in its original form for no profit.
As a creator you can select a Creative Commons license to place on the material you create to let users know exactly how they may use the material.
As a user you'll be able to easily see from a Creative Commons license just what you can do with the material, in terms of sharing, adapting, etc.. If there is not a license, it's best to reach out to the creator to ask how or if you can reuse the material. Creator attribution is always expected.
How do I give Creative Commons works credit and/or get my own license?