multitrack recording with audacity,mixer and computer

I asked a question about laying down one track and then laying down another while you listen to the first.
Well, I got so far as laying one track down and then laying down another next to it after I rewound and then pressed record. However, I just saw
the waveform and did not hear it, so needless to say this method was useless. I did indeed mute all the other inputs (4)
in my mackie mixer but still I could not moniter the first track while I laid another down. Someone also suggested I split tracks
from stereo to mono and I tried that ,to no avail. Any suggestions?

This is difficult to answer because we don’t know which version of Audacity you are using, what your operating system is, or what you have got connected to what.

Assuming that you have everything set up correctly, you need to go to “Edit > Preferences > Audio I/O” and select “play back other tracks while recording new one”.

The comment about splitting from stereo to mono was probably if you are recording two different sources at the same time and then want them as separate tracks - for example, if you record two different instruments at the same time with two microphones and pan one instrument to the left and the other to the right, then splitting the left and right (and setting them to mono) will give you one instrument as one mono track, and the other instrument as another mono track.