Welcome to Using English.
To give you a good answer, it would be helpful to know how much you know about tenses already. Have you studied simple past compared to present perfect, and you just have a question about the specific meaning of THESE sentences? Or have you not yet studied the difference?
Also, I'm not sure what you mean by "missing" a file. For example, was I supposed to be filing all the file foldres in the office, and one is still on the desk, and you say to me "Barb, you missed a file"?
Just a couple more things:
Please try to remember to start your sentences with capital letters.
Please try to remember to put the thing you're asking about in quotes.
What is the difference between "You have missed the file" and "You missed the file"?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.