Ubuntu has its own MySQL build you could use, you can install it through apt-get. This article discusses that and some typically related topics too.
I don't know how the RPM you installed is intended to work, but generally in later versions of Ubuntu, you can use the "service" command to control services. In your case, I'd try:
sudo service mysql start
That should start the mysql service, but, like I said, I don't know for sure what the RPM you installed really does.
I think you really ought to look at the link I provided. You may also quite benefit from installing phpmysql - which can be helpful for administering your mysql server, once you have it running.