وَاعْلَمْ: أَنَّهُ لَا يُعْرَبُ فِي كَلَامِ الْعَرَبِ إِلَّا الِاسْمُ الْمُتَمَكِّنُ وَالْفِعْلُ الْمُضَارِعُ، وَسَيَجِيءُ حُكْمُهُ فِي الْقِسْمِ الثَّانِي إِنْ شَاءَ اللَّهُ تَعَالَى.
Translation: Know that, in Arabic speech, only the fully established/declinable noun and the imperfect verb have iʿrāb. The rule for the latter will come in the book's second major division, God willing.
We are studying noun case first. For now, simply recognize that the imperfect verb may also be inflected; its detailed rules are reserved for the later section.