"In, into, on" The Big Problem

Question

I have always found prepositions to be a fishy part of grammar in English.

Suppose we have a train, a bus, a car, a plane, a ship, a boat.

We can either say:

• To get in the train (bus, car, plane, ship, boat).
• To get into the train (bus, car, plane, ship, boat).
• To get on the train (bus, car, plane, ship, boat).

But what is the big difference between them.

As I feel it:

• "in" shows location and firstly means to get inside of them.
• "into" shows motion rather than the location.
• "on" means to board. But you cannot board "a car" for instance, so it doesn't always work.