Big and confusing, the bus station is part shopping mall. Departures are from the 3rd floor but ticket booths (kassa) and offices for Iranian and Turkish bus companies are hidden on the 1st floor.
For longer routes prepurchasing is wise - an hour before for domestic routes, a couple of days ahead for international routes, notably Istanbul (US$60 to US$70, 32 to 40 hours, several daily at around noon), Tehran (AZN40, around 16 hours, 9am) and Tabriz (AZN25, around 11 hours, 9am). For Tabriz you could alternatively take one of five daily Naxçivan-bound buses (AZN16, 14 hours, kassa 1) and change at Iranian Julfa.
Domestically there are approximately hourly services to Gəncə (AZN9, seven hours), İsmayıllı (AZN4, four hours), Lənkəran (AZN5, five hours), Qırmızı Körpü Georgian border (AZN10, 10 hours), Quba (AZN4, 2½ hours), Qusar for Laza (AZN4, three hours), Şəki (AZN7, 6½ hours mostly via Ağdaş) and Zaqatala. Departure gates are flagged on electronic boards and via www.Navigator.az but accuracy is approximate. Online bookings are theoretically possible up to 10 days ahead via www.bbak.az but that's only available in Azerbaijani.
If the bus to your destination is full, still double-check with the driver or ask at Kassa 7, which deals separately with timetabled minibuses. In addition, if all these are full there will probably still be an untimetabled marshrutka from one of the uncovered bays opposite the main platforms. These services are essentially the only options for some closer or minor destinations and are especially useful for Şəki as untimetabled minibuses take the prettier route via Qәbәlә unlike timetabled services.
The Avtovağzal is nearly 10km north of central Baku. From 2016 the Avtovağzal metro station should become operational. By bus, the most painless approach is to take frequent route 65 from Azneft, İçəri Şəhər, MUM or Beş Mərtəbə. Then at at metro 20 Yanvar or Samaxinka switch to the 16, 37 or 96. Those and other city buses terminate at a parking area accessible through a hidden footbridge from the 2nd floor of the bus-station mall.