systemctl is the control utility for systemd:
http://www.freedesktop.org/software/systemd/man/systemctl.html
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:
http://upstart.ubuntu.com/cookbook/
Once you have a suitable upstart .conf file, you can start a service (equivalent, I think, to systemctl start) using:
start your-service
sudo service network-manager restart
is what I was looking for when I found this.systemctl
(as does any system above Ubuntu 15.04, Debian 8, CentOS 7, Fedora 15...). The old/usr/sbin/service
utility callssystemctl
if/when the system is running systemd.