This depends on the size of the vessel, what the vessels activity is, what the vessel is used for and how it is being used. Need more info.
The red light should be on the right side, or port side, of the boat. The green light should be on the left, or starboard, side of the boat.
From dead ahead to 22.5 degrees abaft the starboard beam
Red
Green
When boating at night, a single white light on a vessel tells you that it is anchored.
When boating at night a red and white light on a vessel tells you that you must give way to the other vessel.
If you see a single white light directly ahead at night then you are the give way vessel.
You are the stand-on vessel but should take precautions in case the other operator doesn't see you.
It depends on its relative bearing and also its proximity.
fishing at night
Starboard ( right side ) and it should be mounted so it is visible at 135 degrees .
you are on the port side of the vessel