My brother works as a Bank teller,seems to me as they work behind the counter
well a teller is an employee of a bank who deals directly with customers.
When did the usage come into existence?
well sometimes they are known as  this employee is known as a cashier or customer representative
That's good! So I believe we are discussion is banking. So when was the first ever banking system establish?
i think that was the 1933 banking act. but now all tellers need experince in handleing cash
OK ,So what other role do they play apart from simply counting cash all day long?
well now most provide on-the-job training.so you will get all the training you need there