The 4 lights on top indicate the battery status. They will light up when you press the round black button once and when you charge your Power+ via the grid.
If the battery status shows only one light, it could be that your Power+ doesn’t have enough power to charge your phone. However, you can still use the flashlight function perfectly fine.
The single light on the top of your device shows if your Power+ is charging from the sun. A single blink means that your WakaWaka is charging slowly (but surely), two consecutive blinks means it is charging faster already and three means it is charging optimally. If it blinks 8 times in a row, it means that it is fully charged.