If someone assists a colleague in difficulty, the recipient should not merely use that person for convenience. Acknowledge the help, pray for the helper, and respond fairly when an obligation remains. The short phrase جَزَاكَ اللَّهُ خَيْرًا expresses a wish for divine reward.
جَزَى concerns recompense and خَيْرًا means good. When addressing a woman, the form may be جَزَاكِ اللَّهُ خَيْرًا; to a group, جَزَاكُمُ اللَّهُ خَيْرًا.
Practical appreciation also involves fulfilling rights. Saying a prayer does not substitute for returning borrowed property, paying an agreed wage, or keeping a promise.