Trains are a mechanic used in Railcraft to keep large groups of carts together as a single 'unit'. Just as a single rail vehicle is a 'cart', a group of carts coupled together is a Train.
To form a Train, the player must bring two carts close together, and then, using the Crowbar, right-click on each. Further carts can be added by right-clicking the last cart on the train, and then the individual cart to be attached. Once linked, the carts will stay together at all times. To separate two carts, the player simply right-clicks each of them with the Crowbar, reversing the process.
Alternatively, carts can be linked or separated automatically through the use of Coupler/Decoupler Tracks. Whenever a Train passes over a Decoupler Track, the cars are separated as though having been manually detached with a Crowbar. Likewise, individual cars that pass over a Coupler Track in close proximity to one another are linked together as a Train.