Creative Commons licensing primarily is a choice of freedoms and conditions. There are also a few additional licenses.
The freedoms are share and remix. Share (by) allows people to copy your work with no modifications. Remix allows people to distribute modifed copies of your work. Remix must be specifically denied (nd).
The conditions are Non-commericial (nc) and Share-alike (sa). Non-commercial prevents people from selling your work. Share-alike is only available when remixing is allowed. It requires people who change your work to distribute their new work with the same license you used.
The possible main licenses are:
by
by nc
by nc sa
by nc nd
by nd
by sa
There are also special licenses. The"sampling" license, which only allows derivitive works to be reproduced, not the original. The "public domain dedication" license, which places the work in to public domain. The "developing nations" license, which is essentialy a "by" license, but with only give these freedoms to those residing in nations not defined as "high income" by the world bank. The "founder's copyright" license, which shortens the copyright (with all rights reserved, as normal) to 14 years, with the option of a 14 year extension (totaling 28 years). Creative Commons also offers "commons deeds", the simplified form of licenses, for the GNU GPL/LGPL.
The Creative Commons licenses are non-exclusive. The author retains all rights to license work under other licenses. The rights given cannot be revoked. It is permissible to remove the license, but those already using the work keep all rights given by the license until they violate it. The licenses do not infringe on fair use and other rights.