Word / formMeaning / explanation
قَالَhe said; the ordinary masculine singular perfect has alif.
قَالُواthey (men) said; a plural perfect form.
قُلْتُI said; an attached subject suffix creates the conditions for medial-radical elision and initial ḍammah.
قُلْنَthey (women) said; the weak letter also drops before this suffix.
قُلْ is an imperative (“say”), whereas قُلْتُ is a first-person perfect (“I said”). Their similar beginnings do not make them the same grammatical form.