What is systemd?

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What is systemd? — provides a standard process for controlling what programs run when a Linux system boots up. 

Starting with Ubuntu 15.04, Upstart will be deprecated in favor of Systemd. With Systemd to manage the services we can do the following:

systemctl start SERVICE

Use it to start a service. Does not persist after reboot.

systemctl stop SERVICE

Use it to stop a service. Does not persist after reboot.

systemctl restart SERVICE

Use it to restart a service.

systemctl reload SERVICE

If the service supports it, it will reload the config files related to it without interrupting any process that is using the service.

systemctl status SERVICE

Shows the status of a service. Tells whether a service is currently running.

systemctl enable SERVICE

Turns the service on, on the next reboot or on the next start event. It persists after reboot.

systemctl disable SERVICE

Turns the service off on the next reboot or on the next stop event. It persists after reboot.

systemctl is-enabled SERVICE

Check if a service is currently configured to start or not on the next reboot.

systemctl is-active SERVICE

Check if a service is currently active.

systemctl show SERVICE

Show all the information about the service.

sudo systemctl mask SERVICE

Completely disable a service by linking it to /dev/null; you cannot start the service manually or enable the service.

sudo systemctl unmask SERVICE

Removes the link to /dev/null and restores the ability to enable and or manually start the service.

I hope this will help you out.

Source:
infoworld.com/article/2832405/what-is-systemd-and-why-does-it-matter-to-linux-users.html

askubuntu.com/questions/19320/how-to-enable-or-disable-services