how to buy bullet train ticket in the counter

First of all, you can search for the schedule on this website.

To buy ticket from the counter, you'd better choose the train you are going to take by searching on this site, write it down, together with your departure and arrival stations (better in Chinese). Upon arriving, give the paper, cash, and your passport to the staff. And I think he/she will understand you.

You are advised to do so just because there is a great possibility the staff do not understand English.