As I sang praise of Otogars with the previous picture here is a view of the Izmir one, of the area between the station proper and the outside facilities.
One has to learn and find one's way inside these monsters. There is some logic in the way the ticket counters are arranged (often by region of destination), and you have to sometimes be impolite to touters who will tell you there is a bus, yes, but not for two hours. They often mean: with the company they send their customers to. Another company may have a bus waiting to leave in a matter of minutes. The large otogars will have luggage storage, toilets, restaurants, in the small regional ones there may be a row of these around a central, dusty courtyard. If there is no luggage facility I never found it a problem to leave luggage at a restaurant or at the office of the company that will take you further, so I could pay a short visit to the city.