To learn about Creative Commons we need to understand how copyright works. Humans are creative beings. We create a lot of things in our lives but there is a fear among us that our works can be stolen and used without our consent. So we have devised a protection mechanism and there is a visible or invisible “all rights reserved” tag (image: left) attached to each of our original creations, which is recognized by different laws all over the world. This is known as copyright.
Copyright is a legal concept, enacted by governments, giving the creator of an original work of authorship exclusive rights to it. The copyright law allows an author to prohibit others from reproducing, adapting, or distributing copies of the author's work. (Source: Wikipedia )
But with the advent of Internet and other new technologies another cultural movement called Open Source  emerged, which is:
“..the creative practice of appropriation and free sharing of found and created content. The rise of open-source culture in the 20th century resulted from a growing tension between creative practices that involve appropriation, and therefore require access to content that is often copyrighted.”
In this culture the users are granted unprecedented access to each other so the Internet allows even greater access to inexpensive digital media and storage. This culture gave rise to the “copyleft ” licenses.
Copyleft may be characterized as a copyright licensing scheme in which an author surrenders some but not all rights under copyright law. Instead of allowing a work to fall completely into the public domain  (where no copyright restrictions are imposed), copyleft allows an author to impose some but not all copyright restrictions on those who want to engage in activities that would otherwise be considered copyright infringement.
The most popular of the copyleft licensing is Creative Commons . Creative Commons licenses are not designed for software, but rather for other kinds of creative works such as websites, scholarship, music, film, photography, literature, courseware, etc.
(Founded in 2001) Creative Commons (CC) is a non-profit organization devoted to expanding the range of creative works available for others to build upon legally and to share. The organization has released several copyright licenses known as Creative Commons licenses.
These licenses allow creators to easily communicate which rights they reserve, and which rights they waive for the benefit of other creators. (Source: Wikipedia )
Here is a video  explaining Creative Commons:
An excerpt from the video:
When you share your creativity you're enabling people anywhere to use it, learn from it, and be inspired by it. If you share your creative wealth, you can accomplish great things. There are millions of other peoples all around the planet who are working together to create a better, richer and more vibrant culture, using creative commons.
In the Global Voices citizen media summit in Budapest  it was a great opportunity for some of us to attend a brief workshop on Creative Commons by Joi Ito , the CEO of Creative Commons and a board member of Global Voices.
Joi said that many use an ‘all rights reserved’ content (photo, text etc.) without consent because they feel that they will not get the permission to use it or it will cost a lot of money which they cannot afford. But they still want to have it and so they become desperate to use it without permission. If most of those works had Creative Commons Licenses the users would be happy to attribute them for non-commercial purposes and link back to the originator. This in turn could promote the work and make it popular as well as retain its commercial value as commercial users would have to buy the permission anyway.
So it is important that we build a culture of licensing our work with creative commons.
The conditions of the Creative Commons Licenses  are explained below:
Attribution (by): Licensees may copy, distribute, display and perform the work and make derivative works based on it only if they give the author or licensor the credits in the manner specified by these.
Use of Creative Commons licensed works – best practices:
Texts and links: When you use some texts or links posted on someone else's blog place it inside inverted comas or use quote tag and link to them. It does not take too long to link, and it is the norm in the blogosphere.
Pictures: Credit the photo to the photographer and include a link to the site by a simple sentence such as ‘Image: (Title) by (Photographer) used under a Creative Commons License’. Link the url of Photo to the ‘Title’, author’s name to the ‘Photographer’ and link the actual license page (if available) to the ‘Creative Commons License’ portion. Don't use the pictures for commercial purposes without consent such as for producing merchandise for sale.
It is always important to give credit where credit is due. This is a detailed guide on “How to provide attribution in the Blogging World “.
Here are some useful links to search contents licensed under Creative Commons:
Related: Working with photos in your Blog .