Source: http://www.arabicgenie.com/2013/05/arabic-question-words 5. ما؟ \ ماذا؟ ma / madha – what? There are two ways to ask “what” in Arabic, i.e. ma and madha. In general, ma is used for questions without a verb, while madha is used when there is a verb in the question. Examples: ما هو سبب غيابك؟ ma huwa sababu ghiyaabik? (What is the reason for your absence?) ماذا سنأكل غدا؟ madha sa-na’kulu ghadan? (What will we eat tomorrow?) The exception to this rule is when you ask “what about?”: ماذا عن الحب؟ madha 3an il-Hubb? (What about love?)

the difference is simple. when you use ما it's used in a sentece without a verb ما هذا؟ ما الجديد؟ ما الاخبار؟ but if your sentence consists a verb so you need to ask by ماذا ماذا تفعل؟ ماذا تريد؟ ماذا يعمل والدك؟ :)