They were small spaces that fit many people because they tried to kill as many people as possible. The people would have to get undressed and put their clothes on places like what above looks like.
The chambers were filled with carbon dioxide and carbon monoxide gases that could kill people, animals, and anything that it was used for.
They were called showers so that the Jews would get tricked into believing that it was fine to go and that they would be safe. When they got in there the lights would turn off so then they would have no way to leave after that.