How to connect my laptop to my UD-M30 Denon hifi to play music?

Hi,

I've got the right cable to connect my laptop to my denon hifi and have plugged the red & white cable into the 'Line 2 IN' sockets at the back, but was told i then need to 'select MD' - I don't know how to select MD or even what this means and I don't know which function the denon should be on - radio or cd? Please help!