Hello, the common English expression is "Can't find your way out of a paper bag". A common example would be if I was frustrated with a particular person, by their inability to perform some simple task...in my frustration I might say "he can't find his way out of a paper bag!" or "he couldn't find his way out of a paper bag!" A boss might say "he did nothing on this project, he can't find his way out of a paper bag!" Because it would be a SIMPLE task to "get out of a bag", so to speak, this expression is an hyperbole---not to be taken literally, but to express my disbelief, my frustration, my exacerbation, with some person's lack of effort, lack of action! I suppose the expression uses "paper" in particular, because it is an old expression, in the days when most bags were paper and not plastic. I hope that this helps, feel free to ask for any clarification. Best of luck with your language studies!