Reading and understanding your publication agreement (sometimes called a copyright transfer agreement) is important to make sure that your work can have the widest distribution possible and that you retain all of the rights you want. For example, some traditional publication agreements prevent you from distributing the work to colleagues, including a portion in a future publication, meet grant requirements for open access, or placing a copy on your website. Some agreements can be very short and may not detail the rights you are signing away. Here is an example of one such agreement:
"The author hereby assigns to ___________ the copyright in the above article, throughout the world, in any form, in any language, for the full term of copyright, effective upon acceptance for publication."
SHERPA/RoMEO summarizes journal copyright transfers and permissions. It also ranks the journals on a color scale to easily show authors if pre- and post-prints of an accepted article can be published or stored elsewhere.
In the example below, if I publish an article in the Journal of Popular Culture, I can post the version before it underwent peer-review (pre-print) somewhere, provided I acknowledge where it is being published. For the reviewed version, I have to wait 2 years (embargo) before posting it in selected places. And I'm never allowed to post the publisher's formatted PDF copy anywhere.
Creative Commons licenses are a way to modify and indicate how others can use your content. This can be used to signal to others that they don't need to ask to remix something you've created, provided they include attribution. The licenses standardize ways to give the public permission to share and use your work on the conditions of your choice. These licenses are not an alternative to copyright and work alongside copyright.