How do I start/stop or enable/disable services with systemd?
Activates a service immediately:

systemctl start foo

Deactivates a service immediately:

systemctl stop foo

Restarts a service:

systemctl restart foo

Shows status of a service including whether it is running or not:

systemctl status foo

Enables a service to be started on bootup:

systemctl enable foo

Disables a service to not start during bootup:

systemctl disable foo

Prevent a service from starting dynamically or even manually unless unmasked:

systemctl mask foo

Check whether a service is already enabled or not:

systemctl is-enabled foo