While they were there, the time came for the baby to be born, and she gave birth to her firstborn, a son. She wrapped him in cloths and placed him in a manger, because there was no guest room available for them. Luke 2:7

A manger is a feeding trough used to feed livestock (sheep, goats, cows). The size of the manger makes it a perfect fit for a newborn baby.
This indicates that Mary and Joseph were given a place to sleep associated more with animals than humans. It could have been a barn-like structure separate from a house, a cave where animals were kept for protection and warmth, or a basement room in a house where the animals were brought into when it got cold.

All of it communicates the humble conditions Jesus entered this world, not in a palace or a hospital with a neonatal staff. He entered the world as most people do then and now, in unclean surroundings, lonely and abandoned, but very much under the watchful eye of God.