You cannot, it is there for pure story.
ride the magnet train
If you mean the magnet train it's in saffron city and goldenrod city.
The Johto Region is not apart of the FireRed/LeafGreen games, thus GoldenRod City is not in the game. Plus, the Magnet Train isn't built to link Saffron City and Goldenrod City for 3 years later AFTER the time when FireRed/LeafGreen takes place.
The magnet train stations are located in Goldenrod and Saffron city.
if you are in kanto it is in saffron city but if you are in jhoto its in goldenrod city
Goldenrod City
It is in Goldenrod city, but there is also one that is in Kanto.
the magnet train is in Goldenrod city and saffron city. you can use the magnet train once you have beaten all 16 gyms
If you are in goldenrod, take the magnet train and you will be in saffron
the train takes you from goldenrod to saffron city and then the same way backwards ( you need the train pass before going on the train)
Anywhere near the 3rd gym's city which is goldenrod city.
You get an eevee from bill in goldenrod city and train it till it evolves.