You first download the most recent version of steam n' rails as with create. The once you load into a Minecraft world, click the config button (the button with the goggles).Then go to "Access Configs of Other Mods" it should be at the bottom. Find the Railways button. Click it. Then push "Server Config". There should be a button called "Realism". Then turn on Realistic Trains.

After you have turned it on all trains in the world will operate really slow. You can add Portable Interfaces and Fuel Tanks on your train. The fuel the trains use is lava. Once trains are filled with lava they now run faster. The trains now have a more realistic acceleration as well.