The three masculine third-person forms refer to one man, two men, or a group of men. The same number distinction appears in the corresponding passive forms.
FormActivePassive
Singularفَعَلَ: he did.فُعِلَ: he was acted upon.
Dualفَعَلَا: they two did.فُعِلَا: those two were acted upon.
Pluralفَعَلُوا: they did.فُعِلُوا: they were acted upon.
The final ـا marks the dual and ـوا marks this masculine plural. Active identifies the doer; passive expresses the action as experienced by its grammatical subject.