Steam is dead in Cuba. The only operations are at a few tourist "museums", generally run by local economic groups trying to use local assets to attract foreign dollars. Parque Lenin at the south end of Havana sometimes has steam running on the park railroad.
For passenger trains, there are several routes that run in and out of the Havana area. The schedules can be hard to find, but the main east-west trains generally run daily, with a night train and a day train. Locals are much more iffy. Regular service still exists on much of the Hershey line east out of the east side of Havana.
If you have never been to Cuba, tours are often the best option. Looking for steam, go on a rail tour as they often can charter steam on a few lines. There have also been some attempts to have organized steam events across the country, but with little success. You can also hire local guides, but they seldom will get you anything more than the local tourism, which normally doesn't include trains.
There are several internet sites that try to report on what is going on, check them out for details.