Okay, so here is how I recorded the introduction to Kansas' "Carry on Wayward Son" with just me, myself and I (meaning it was just my voice singing all the parts).
First, take a listen to how it came out:
1. I opened my audio recording software, Reaper (see my post on Reaper here) on my computer.
2. I hit the "Record" button in Reaper and sang the melody (the high part:)) into the microphone, which was a Rode NT2-A. The mic was connected to the computer via an audio interface box like the Focusrite Scarlett 2i2.
3. When I finished singing that high part, I inserted another track in Reaper (ctrl-T) and sang that part again, giving me two tracks of my voice singing the same thing.
4. I inserted a 3rd & 4th track and repeated steps 1-2, but singing the middle vocal harmony part.
5. I inserted a 5th and 6th track and repeated steps 1-2, but singing the low vocal harmony part, "low" being extremely relative in this case;).
6. I edited each of the 6 tracks with my audio editing software, called Adobe Audition. Editing consisted of getting rid of "p-pops" and various other mouth-y noises, as well as making sure none of the notes were off-pitch.
7. Back in Reaper, I panned each track to a specific place in the "stereo spectrum," which is a fancy way of saying "somewhere between your left ear and your right ear." both high parts were in the center (right in front of you, between your eyes (actually they were 5% left and 5% right, but they'll sound like they're coming from right in front of you). The two middle parts were panned 100% left ("hard left") and 100% right (yup, "hard right") respectively. If listened to by themselves it would sound like one was coming from your left and the other coming from your right. The low parts were panned 53% left and right, respectively. These would sound like they were between the guy singing the high part and the guy singing the middle part, kinda like 6 guys were spread out in front of you on a stage. See the figure 1.
8. The next step was to make sure each part was the right volume, not too loud and not to quiet. That's called mixing, and you do it by adjusting the volume slider on each track so all the sounds work and play well together.
9. Next I added a reverb effect to the "master" channel.
10. I rendered (called "mixing down" in the old days) the project audio down to one stereo file, which I saved as an mp3, and voila.
Ta for now!