Ubuntu doesn’t come with ssh. You simply have to install it via the software center or apt-get, the package name is openssh-server.
You may also change the config in /etc/ssh/sshd_config (and run “/etc/init.d/ssh restart” to apply the changes immediately). Remember that even when secured, ssh is a door into your machine. Use it preferably if you’re not connected directly to the internet (on a private network). I might enrich this post later to explain the ways of securing it (to some extend).