Not a stupid question. "what did you do yesterday" is the structure you need to ask a question and can end with a "?". "tell me what you did yesterday" can't end with a "?" because its not a question. It's more of an an order.. :) If you break the sentence with a comma you have: "tell me, what did you do yesterday"?

You can say this, but you need a (,) and a pause. For example: "Tell me, what did you do yesterday?"

Firstly, it is not a stupid question! All of your examples are correct! You just need a comma in the last one: "Tell me, what did you do yesterday?".

Hey Dorka. You are welcome to send me a message.

never any stupid questions when it comes to learning another language, I am no teacher, but nothing wrong with the questions " what did you do yesterday? or " tell me what you did yesterday ( more of a direct order then a question". I just find people have a different preference to get their meaning across :). Feel free to message if you want to talk :)