if a ticket was purchased in advance, it is almost always required to check in at the company's window with id and/or passport first to get the actual printed ticket from the bus company - after getting a ticket, it is necessary to locate the platform where the bus will be picking up passengers. 

the bus stations usually have simple directional signs showing platform number ranges with arrows leading to their locations - a bus may not always park in the exact platform number as indicated on the ticket, therefore if it appears the bus is not present near departure time, take a look at the nearby platforms for buses of the same company and destination.