Hello, Mostafa. When we say 'what did you do?' we are talking about one (specific) time in the past. We are asking about one action, which started and finished in the past. We're using the present simple tense. When we say 'what have you done?' we are talking about a time in the past - but it's not specific. We are asking about either one action that you did, but the specific time isn't important, or we're asking about more than one action in the past. We are asking for more of an explanation. We want to know more information. We're using the present perfect tense. A: 'What did you do yesterday evening?' B: 'I went out for dinner and watched a movie.' [ NOT 'I have went out for dinner and a movie'] A: 'What have you done today?' [no specific time - any time today] B: 'I've done my homework, been for a walk, and washed the dishes.' ['I did my homework, went for a walk, and washed the dishes' is also okay.] There is also a difference in tone: 'What did you do?' can sound concerned or irritated. A: 'What did you do?' [concern - same as 'what happened?'] B: 'I fell off my bike, and cut my leg.' A: 'What did you do? [irritation] B: 'I was drinking coffee, and accidentally knocked it onto your homework.' 'What have you done?' can sound angry. A: 'What have you done?' B: 'Sorry, I accidentally knocked my coffee onto your homework.' A: 'That's due tomorrow! I've spent hours writing that!'