What's the difference between 'on the train' and 'by train?' [closed]

While studying, I faced these two sentences:

I come to Istanbul on the train every week.

and

I came to Istanbul last week by train.

I want to know is there any differences between the phrases 'on the train' and 'by the train?'

Regards

Solution 1:

On means you are physically on the train. By is referring to the method you used to get to Istanbul (ie train).