Hi! We use Simple Past ("I did") for finished events, while Present Perfect ("I have done") is used for events that are still in progress or they still have an effect on the present, I did my homework yesterday. (finished action) I have just done my assignments. (I finished it a few seconds/minutes ago - it has an effect on the present) Have you done the housework yet? - Yes, I did it yesterday. Hope this helps.

Also, "I did" focuses on the event of completion, while "I have done" focuses more on the time it takes to do it. "I did my homework" means I finished it "I have done my homework" implies that it took me some time to finish it