أَكْتُبُ الدَّرْسَ.
Meaning: I write the lesson.
Parsing: aktubu is an indicative present verb; its subject is the obligatorily concealed anā; ad-darsa is the direct object.
نَكْتُبُ الدَّرْسَ.
Naktubu is an indicative present verb; its obligatorily concealed subject is naḥnu; ad-darsa is the object.