take a tube or pipe which is not very thin and also not very thick.it should be of medium thickness.
now take two paper cups.attach one cup to one end of the pipe and the other one on the other end of the pipe.
note : there should be no gap or any open space during attaching the two paper cups to the ends of the pipe.
now your stethoscope is ready.
you can use it to confirm that it is working.