Want to travel on 7th September from Hangzhou to Beijing. Which station I have to use at Hangzhou

Which kind of trains do you want to take, the high speed trains (G-trains) or the ordinary trains?
For G-trains, you need to go to Hangzhou East Railway Station and for ordinary train, you need to go to HZ Railway Station.
If you have already booked the train tickets online, you just go to the local railway station go get your ticket by using your passport.
If you did not buy your tickets, you can go to the local railway station to buy one with your passport. You need to buy in advance.