뭐 했어요? Vs 뭐 한 거예요?

When do you use 뭐 했어요?
When do you use 뭐 한 거예요?

Question

뭐 했어요? Vs 뭐 한 거예요?

When do you use 뭐 했어요?
When do you use 뭐 한 거예요?

Answer

뭐 했어요: means: "What did you do?" It's a past tense form.
뭐 할 거예요: means: "What are you going to do?" It's a future form.

Answer

V + -(으)ㄴ 거예요 used for the action what the speaker has some information.
V + -었어요 used for the action what the speaker has no information.

뭐 한 거예요? : What is that you did? (The speaker saw some actions or heard some noises.)
뭐 했어요? : What did you do? (The speaker has no information)