01 Oldsmobile aurara headlight is out at night... but during the day it works??? Don't understand

You are seeing the DAYTIME RUNNING LIGHT when it is day-time .. At night the actual HEADLIGHT must revive voltage from the headlight circuit - that circuit is FUSED.. Here is a link to a diagram of the fuse box - look at the diagram to find the suspected fuse. https://www.autogenius.info/oldsmobile-aurora-2001-fuse-box-diagram/ Good luck!