To out in basic terms, a mono mix has the same sound coming out of the left speaker as whats coming out of the right. Like so:
L&R speakers: John (guitars & vocals)) Paul (Bass, piano and vocals)George (guitars and vocals) Ringo (drums and percussion and vocals)
Where as stereo has the sound separation and remixing which makes this possible:
L: John (Vocal dub 1 and harmony, and guitar dub 1,3,5) Paul (vocal dub 1 and harmony Bass dub 1,2) George (lead guitar, guitar dub 1, background vocals) and Ringo (Drum dub 1)
R: John (vocal dub 2 & 3 with guitar dub 2&4) Paul Vocal dub 2&3 and bass dub 2) George (guitar deb 3&4) and Ringo (drum dub 2&3 with percussion track)
You can only imagine the level of seperation if the mix is 5.1 or 7.1 instead of 2.1 (stereo).
Does that make sense?