If we want to say how we travel from one place to another we use the preposition BY:

- I go to work by car
- He went to Salamanca by train
- We will travel to Moscow by plane
- We went to Greece by boat

But we say: I go to work on foot  (= walking)

You get in or out of a car
- He got in the car and left.
- When we were going to Oxford I had to stop and she got out of the car because she was feeling very dizzy.

You get on/off a bicycle or public transport (public transport is a means of transport designed to carry many people)
- The hill was too steep, so I got off my bicycle and continued on foot
- Get on the bus, it's late.
- (on the bus) This is my stop, I'll get off here
- There are 1200 people on this ship
- When I'm on a plain I always fall asleep  (you can't say: I'm in a plain)