Basically, what title says. If you never played Terraria tho...
When you right-click with empty hand on rails tracks, there will be a minecart spawned, and you will be automatically placed in that minecart.
The beauty is, this minecart does NOT have any drag, thus it does NOT slow down over time. That means no more those annoying booster tracks every 20 blocks! Cart will despawn when empty and stopped. Otherwise it behaves like a usual cart. But with no need for boosters, yay!
FOR TERRACART 1.12.2 SEE https://minecraft.curseforge.com/projects/terracart-reloaded by Kreezxil