你真好用英语可以译作 "You are very useful." 这句话的来源可能源自对某个人或物品表示赞赏，因为它对某件事情有帮助。例句：

"You are very useful in helping me with my homework." (你在帮我做作业方面真的很有帮助。)

"This tool is very useful for fixing things around the house." (这个工具在修理家里的东西方面非常有用。)