Correctly Using ACS712 hooked to a microcontroller
Before any testing, prevent touching the pcb accidentally by packing the module in a suitable plastic box.
The ACS series convert current[AMPERES].
If you need power[watts] measurement you need to add a voltage measurement and do some extra calculations in the controller.
The two screws are MAIN-side.
Capacitors are needed to adjust filtering behaviour.
The ground from the mains is not needed for the current-measurement.
The ground pin from the mains should be used, for safety reason, to ground all outer metal parts that can accidentally contact one of the main wires.