This link works for Ubuntu 10 https://launchpad.net/+help-registry/openpgp-keys.html#publish How can I do this in Ubuntu 12.10 because its different in Ubuntu 12.10.
Using the command-line to publish your key you can run,
and then you should get the following notification:
You can check it is present on the server by running the command given in this article:
You can also use the gui program,
A more recent gpg tutorial is available at Ubuntu help, which goes through in some detail how to create, publish, and backup your GPG keys.