A Sample of Systemd Service Script

On Debian Jessie, the path of the file is:
/lib/systemd/system/ghost@.service

[Unit]
Description=Ghost Blog Server  
After=network.target

[Service]
Type=simple  
User=ghost  
WorkingDirectory=/var/www/%i  
ExecStart=/usr/bin/npm start --production

[Install]
WantedBy=multi-user.target  

The "%i" in the script means the argument given by the user.
For example:
systemctl start ghost@sample.service The "sample" will be given to the "%i".