دَخَلَ الطَّالِبُ مُبْتَسِمًا
Translation: The student entered smiling.
دَخَلَ: past verb.
الطَّالِبُ: nominative subject and ḥāl referent.
مُبْتَسِمًا: indefinite accusative ḥāl describing the student’s condition while entering.
This is a new practice example, not a quotation from the textbook.