2nd Station (as well as 3rd, 4th and 5th Stations) should be used for further development – building new city and increasing your passengers spawn rate, maximize amount of passengers and thus even gold for your contracts or friends.
You can also redirect here all Express trains from Mr. Bill and International trains from your friends if you place there two special buildings- Train Yard Tower and Switch Outpost.
You however cannot dispatch any trains from it. You can do that only from your main station.
Here you can also find more information about
*edit 220818; added links to Train Yard Tower and Switch Outpost wiki pages. Tidied up 2nd to 5th station links - Sc00by