Small red and black are power for the meter, ideally it should be floating with respect to the measurement circuit.
White is current IN to the meter, Large Black is current OUT from the meter.
BOTH BLACKS ARE CONNECTED, this type of meter is not isolated, it is for LOW SIDE measurement unless your power supply to the meter is floating.
If you use the same power supply for powering the meter, as for powering the circuit, at least in the ones I've used, the accuracy is terrible.