This is a DC controlled Solid State Relay which can turn 230V AC equipment on and off. The output is like a NO normally open contacts of a relay and have to be in series with the Load like any other switch.
This should not be used for large inductive loads like big motors. The Q1 transistor limits the current thru the LED by providing an alternate path for more current. The DC input can be from 3V to 20V.
The Triac can be chosen depending on current in the load. Look for datasheets and applications at STMicroelectronics for BTA41600 triacs. MOC3041 zero crossover opto-diacs.
Read more at my main page - Solid State Relays - SSR I used to make them long ago.