systemctl is the control utility for systemd:
Note that Ubuntu doesn't use systemd, it uses upstart, which does a few of the same things in principle, but has some different concepts.
Without much knowledge about systemd, and based on what I read in the document I posted, I think you don't need to "enable" a service. Just dropping the .conf file for your service in /etc/init should make upstart aware of it.
That's the crux of the matter, though: the systemd config file for your service won't work unmodified on Ubuntu, you have to "translate" that to an equivalent version for Upstart. Here's documentation for upstart:
Once you have a suitable upstart .conf file, you can start a service (equivalent, I think, to systemctl start) using: