I want to travel by train from Beijing to xi'an. Where can I buy a ticket?

Oh, you can buy it at any train stations. From BJ West Railway Station, there are 13 trains available from 07:00 to 05:15. If they have enough ticketm, buy a ticket at least 40 minutes ahead of a specific schedule. You do not need to a Chinese speaker, the ticketing staff can speak simple English. You will get your ticket easily.

And this is a hot high rail route, so it is best to book ticket in advance. The reservation is available 60 days ahead of the schedules. You can turn to an agent like Travel China Guide without worrying about the language problem.