You must plug the RCA cable (matching white with white, red with red) to the tape in on the mixer.
You can plug this cable into any line in input on the mixer (1-8, L, MONO).
You can plug this cable into any stereo in input on the mixer (3-8, L+R, STEREO).
Make sure the main fader is turned up when using line in inputs and the tape level knob is turned up when using the tape input. Also, you will see signal on the meter if your sound is working. If you don't see signal, there may be a faulty cable, microphone, or your device isn't playing anything.
Main level and tape level 
Signal Meter