If your tv or hifi have phono inputs for left and right audio, then use a "Y" audio lead this has a headphone plug at one end for the MP3 player output and 2 phono plugs at the other end (usually red and black or white and black). These plug into the "Audio In" sockets on your tv/hifi.
Phono plugs and sockets are coaxial meaning one centre pin surrounded by a tube like shield.
Yobbo, April 2013