The recording below has been done multi-track i.e. each instrument has been recorded separately on its own track. It starts off with just the raw recorded tracks, and while it's been recorded reasonably well, the guitars are wimpy, the bass is getting lost in the mix, and the vocals just don't cut through.
Half-way through, the recording switches over to the mixed version and the difference is enormous. The guitars sound huge, the bass is thumping away with the kick drum, the snare drum is cracking and the vocals have much more presence.
Once a track has been mixed and is sounding good, it's ready to be mastered, to make it sound great!