That station worker realized he forgot to stop the steam train.
It was my favorite steam engine, so I took thousands of photos.
"Excuse me, how often do the steam trains come?" "About every twenty minutes."
A steam car is a car that runs on steam. No regular car runs on steam, but what thing that has things called "cars" does run on steam? How about a steam train? You can also think about 電車s, which are electric cars (but means "train"). This is similar to that, but now it's run with steam, making it a steam train.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.