It depends on its relative bearing and also its proximity.
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.
fishing at night
You are boating at night you see a single white light directly ahead, you should give way by going around the other vessel.
you are on the port side of the vessel
You are the stand-on vessel but should take precautions in case the other operator doesn't see you.
A white light is the color of light that must be displayed on a vessel towing at night, I t must be displayed at 8.2 feet higher than the colored sidelights. It should have an all round white light visible for 2 miles.
another vessel is at anchor
The green light would be the starboard steaming light, the white the masthead light. What you would do would depend on factors such as its releative bearing and in what waters you are sailing.
The masthead light is typically white in color. It is displayed at the top of a vessel to indicate the presence of another vessel at night.
The head and starboard side of the vessel is toward you