To start a service, use the systemctl start command:

sudo systemctl start sshd

To stop a service, use the systemctl stop command:

sudo systemctl stop sshd

Changing the state of a service only lasts while the system remains at the same state. If you stop a service and then change the system-state target to one in which the service is configured to run (for example, by rebooting the system), the service restarts. Similarly, starting a service doesn't enable the service to start following a reboot. See Enabling and Disabling Services.