عَمِلْنَا = عَمِلَ + ـْنَا
The basic verb gives ‘acted’; the ending identifies ‘we.’
حَمِدَتْ = حَمِدَ + ـَتْ
The ending identifies one female doer: ‘she praised.’
حَفِظُوا = حَفِظَ + ـُوا
The ending identifies masculine plural third person: ‘the men memorized.’