Stems are the collection of individual tracks that you mix together. I can't listen right now, but I think you've got three tracks; two guitar tracks and a bass(?) track, so three files that should be the exact same length and size (same sampling rate). Some digital audio workspace softwares have the equivalent of an auto-generate stems command, where the software just outputs each track, but I dunno how to do it for anything other than Ableton. Fuckin' YouTube tutorials are always my best friend for stuff like this.
Do you have a mic'd drum kit??? I'm kinda jealous b/c the feel of real drums is so hard to mimic, but I think I'd just end up triggering MIDI drums to the actual drums, which is generally perilous and rarely works live, and I'm still trying to stay inside that restriction.
You're talented in the realm of composition. The realm of production know-how is so much more accessible these days. Composition know-how is not so straightforward, or even well-defined.