The metro runs frequently. When you come out of the otogar terminal with your back to it you turn left and immediately after the buiding finishes you take a left turning. It is sign posted for Antray. Its about a 5 minute walk to the metro station. There are 2 services. One is to the otogar and one to Expo. The metro has an info board whiche tells you when the next metro arrives and if it is expo or otogar. Once on the metro there is an information board with the next station showing and a verbal bulletin too. Its very easy , extremely smooth and there are plenty of seats. You can buy your ticket at the metro station , too.
WW