Where to get the shuttle bus to Terracotta Army?

I had a hard time finding where the shuttle bus was, and how it works. The bus is free IF you keep your train ticket coming into the North Train station (they allowed me to show my confirmation on my phone), and you buy your entry tickets there. The information center does not sell tickets. I asked multiple times. There is a booth at the south side of the station (if your facing south it’s on the right side), called Northwest International Travel Service. I was able to show my train ticket confirmation, my passport, and buy the ticket.