This is a Normally Closed PCB Mount SSR. That means when DC Control input is low, the triac is ON, the output passes the load current to turn on small heater-motor-lamp or a bigger contacter-drive etc.
When input DC is high the output is OFF. This is also Optically Isolated from
Mains. A Microcontroller output which is buffered by some driver can drive this
relay. It is better that in big systems these SSR Modules can be on another PCB,
to avoid mains wiring near Logic circuits. But this cannot be used for medical
electronics, or critical applications. More reliability and visual isolation of
voltages may be required for such equipment.
AC Load SSR DC control