The Terminal is divided into several sections (all color coded) with their own respective small waiting areas. There are TV monitors that show the departure information and platforms along with a muffled overhead anouncement system. The exact platform/gate will be announced very close to departure. However they will give you a range of platform/gates when purchasing the tickets. Othewise there is an info booth close to the front end of the terminal. Its not a fancy place so plan your arrival time accordingly .. To put things in perspective, its about a 5 minute walk from one end to another.. Departures are In one area and arrivals in another (and ticketing) is a level above. Hope this helps..

https://en.wikipedia.org/wiki/Retiro_bus_station