رَأَيْتُ زَيْدًا.
Translation: I saw Zayd.
Grammatical analysis
رَأَيْتُ: past-tense verb; the final تُ is the subject pronoun, “I.”
زَيْدًا: direct object, accusative with a visible fatḥa.
Zayd is the person seen. The word therefore appears as زَيْدًا. The written alif accompanying accusative tanwīn is not itself the primary case sign; that sign is fatḥa.