An engine heads a trains, with cars behind it, and the caboose the last car.
NOTE: If a train is heavy with freight, it may have several engine 'cars' pulling it, AND even pushing it from the back.
NOTE: There are several types of train "cars".
The engine. The driver is called the engineer.
If it's a powered locomotive, then a locomotive. If it's a car with a cab to control the train, then a cab-car. If it's a train powered by itself, called a Multiple Unit (MU) with the engine part of the train, the front is called, well, the head end.
The front part of a hat is the brim.
Each part of a train is called a car.
engine
Front part of a Baseball is called "peak", i.e. the stiff front part of a cap that sticks out above you eyes.
The front part of a ship is called the bow.
A locomotive is what supplies the power. A locomotive can in itself be considered a train depending on its function. A cowcatcher!
The fairing.
Usually The front part of the stage is called the downstage! I think the questions refers to the part of a stage in front of the curtain.. referred to as the "apron". Hope this helps
The front of a regular train is usually pulled by a locomotive. This is the powerhouse of the train. If your train doesn't have a locomotive, but looks like cars with a window for the train crew, then that can be called the cab car, or as you put it, "the head of a train". There isn't any slang (that I know of) used to call it something special. I uses "front of train", but "head" sounds better. We do shorten "locomotive" to just "loco".
The Driver of the train usually sits at the front of the train