Trains are made up of two main parts: the engine and the carriages.
The engine is like the strong heart of the train. It gives the train the power to move. When the train starts, the engine pulls the carriages behind it. These carriages can carry people, called passengers, or they can carry things, known as cargo.
So, when we say, 'The engine pulls passenger carriages or cargo,' we mean that the powerful engine at the front is pulling everything that follows it, making it possible for people to travel or for goods to be delivered!