there are many rules to master this thing for example if the word is located after مِن ، على ، الى the word will end with Qasra Example : مِنَ البابِ from the door , على الطاولةِ on the desktop , الى المدرسةِ　to the school the word after حيثُ is always Damma حيثُ المدرسةُ the basic phrase in arabic should be as : Verb + Subject + Object the Subject after the verb ends in most cases with Damma and the Object Fatha For example : أكلَ أحمدُ الموزَ Ahmed are the banana There are a lot of rules , if you learn them a lot , you will master this :D

It depends on عَامِل عامل is a word which effects a change in the case-ending of a neighbouring word in a sentence, e.g., in في بيتِ المدرسِ, the word في has changed بيت from مرفوع to مجرور, and in قرأتُ كِتابَ عمر, the word قرأ has changed كتاب from مرفوع to منصوب. In the first example في is عامل.

usually at the end of the word you put damma, fatha, or kasra, hope that helps