Okay kiddo, so a railroad chapel car is a special train car that is like a tiny church on wheels. It was used a long time ago, when people would travel across the country by train and didn't have a church nearby.
The railroad chapel car had everything you'd find in a regular church, like seats for people to sit on, an altar where the preacher would stand, and even a little bell to ring when it was time for the service to start.
The chapel car would be driven to different towns and cities along the railroad tracks, and people would come to attend church there. The preacher would give a sermon, sing hymns, and offer prayers, just like at any other church.
It was a really cool way to bring church to people who might not have been able to go to one otherwise, and it helped bring communities together along the railroad lines.