زَيْدٌ قَائِمٌ
Translation: Zayd is standing.
إِنَّ زَيْدًا قَائِمٌ
Translation: Indeed, Zayd is standing.
«زَيْدٌ» is the nominative mubtadaʾ before entry; «زَيْدًا» becomes accusative ism inna afterward. «قَائِمٌ» stays nominative as khabar. «إِنَّ» adds emphasis.