I am confused about the timing of salah. To join salah how should I do it? So when the azan for zuhr comes then I can pray zuhr and asr? Or can I wait for asr azan and then pray zuhr and asr? Same for maghrib do I pray at maghrib azan or after isha azan both maghrib and isha salah?

You pray once the Azan for Zhur is done. You don’t have to wait for Asr. Likewise in the case of Magrib