Put one lead on the green connection and one on the black: what does your meter say?
Put one lead on the green and one on the red: what does your meter say?
there should not be any power to the white connection, it is the neutral wire. Don't bother with it.
If you get readings, you at least know you have power to that point. If you get nothing, trace the wires back to a previous connection and test again, same process. You need to find where power starts/stops.
This is electricity 101. If you get power in the first tests I typed, the other pinhead shere can tell you how to test the right side of your pic. I'm assuming that box is an inverter, but I'm not sure.