• You can walk from bus station, very close by, 10 minutes.
• If you are at the Noi Bai airport, buses will pick you up from there, you don't need to go to Hanoi center which is 30 km far away.
• There is no train yet from Hanoi capital to Ha Giang, the only way is by sleeper bus or cabin bus. $9/ticket, very cheap, you pay as local.