In English, a word stays exactly the same no matter what its "job" is in the sentence. "I see a book. The book is green."
But in Arabic, the very last sound of a noun changes depending on its job! This is called I'rab (Grammatical Case). Let's meet the three states.
This is the natural, default state of every noun before anything interacts with it. Subjects and Predicates are always Marfoo'.
This state is activated when a noun is the target of an action (the Direct Object). Notice that it usually requires an extra Alif to hold the sound!
This state is activated when a noun comes directly after a preposition (like "in" or "on").
Did you notice the Mansoob case? When a word is indefinite (no AL) and gets the double Fathah (Fathatayn), it is so heavy that we have to add an extra Alif (ا) to hold it up! Let's see it in action:
For the rest of this level, until we dive into Prepositions and Verbs, we will be working primarily with the natural, peaceful Marfoo' state. Remember this Golden Rule:
If nothing has attacked or altered the noun, it is Marfoo'.