Night can be one of the worst times in your minecraft world if not prepared. After gathering some wood and makes some basic tools it would be best to dig a little hole in the side of a hill or mountain. Or just create the classic dirt house we all know and love.
After you create your little living space for the moment, try to make a firnace to get some charcoal if you didn't find any during the day. Torches are an essential for the first days in your world. Dont for get a bed to sleep the night away.
When you feel more comftorable with your world you can go around your world at night and fight the hostile mobs to then get resorces and xp to level up.