How to Link Carts Together into a Train
Coupling lets you pull multiple carts with a single powered engine, which is how you move bulk cargo or carry passengers without running a separate line for each cart. The exact coupling item depends on the mod version, but the principle is the same: you connect carts end to end so they move as one unit.
Building the Train
Place your lead cart first, then place the cart you want to pull directly behind it on the same track. Use the coupling action on the two carts to link them. Repeat for each additional cart. Once linked, only the front cart needs to be powered; the rest follow it. Keep the whole train on the same rail line and avoid sharp turns, since long trains can derail or clip through blocks at tight corners.
Running and Uncoupling
Give the front cart a push with a powered rail or launch it from a station, and the whole train should move together. If a cart in the middle refuses to follow, uncouple and recouple it; a bad link is usually the cause. To break the train apart, use the same coupling action on the joint you want to release. Store spare carts on a siding so you can add or remove them without blocking the main line.