Qusar is about 175km northwest of Baku, a drive of roughly two to two-and-a-half hours on the main road north. The road is paved and in reasonable condition; the last stretch through the Caucasus foothills is scenic.
From Baku: Shared taxis (marshrutkas) depart from the Avtovagzal (central bus terminal) in Baku. Ask for the vehicle going to Qusar or Gusar; departure times are usually mid-morning, and the fare is cheap. The journey takes around two hours. There are no scheduled buses. You can also hire a private taxi for a fixed price; negotiate before getting in.
From Quba: Quba is the nearest sizeable town, about 25km south across the river. Regular shared taxis run between the two towns and the journey takes under 30 minutes. Most travellers pass through Quba first. From Qusar, the Shahdag mountain road continues 29km to the ski resort and Laza village.