how did the Arabs treat people they conquered?

Answer 1

While its hard to put a generalized response to this question that covers all the bases, generally, Arab conquests resulted in relatively decent treatment for those that succumbed to their rule and agreed to pay their new taxes (which, in some cases, like that of the former Byzantine lands) were less burdensome than the Arab taxes. Further, you should know that Christians and Jews ("People of the Book") were known as 'dhimmi' populations, or, tolerated populations. They were made to pay the jizya tax but otherwise could live their lives and worship freely.