Not much these days is completely free, but copyright is both free and automatic. Copyright involves your moral authority to assert that you are the creator of your work.
copyright lasts for seventy years after the death of the author. So if you have
written that bestseller, make sure you have made arrangements in your will so
that these rights are appropriately managed.
http://www.copyright.com.au/ to enable others to appropriately seek and pay for licensing/using your work.
Alternately you may wish to make your work public and free for anyone to use. If this is your preference, consider using Creative Commons http://creativecommons.org.au/