Live Recording vs. Studio Recording.
Lets say you would like to record an original guitar and vocal composition.
One popular way to record a live performance like this would be to place one microphone on your guitar and another on your vocals and simply record it live to "Two Track Stereo". In this case, you would play your song from beginning to end and hope you don't make mistakes along the way. If you're happy with your entire performance, I can simply burn you a CD and your on your way. However, if your guitar performance was flawless but your vocals were flat, then you'll probably want to rerecord the song all the way through again and hope your happy with the next pass. This approach is similar in scope to the early recordings of the 1940's 50's and 60's where they had to play, over and over again, until they got it right. This approach is still popular in some circles today but you must be well rehearsed and have a lot of endurance.
So, that works great for live recordings but, what if your vocals do end-up requiring pitch correction or later-on you decide you want to add reverb to the guitar but not to the vocals? This is an ultra simplistic example but it illustrates a real world scenario. If you want that kind of flexibility then the live approach is not the way to go. The problem is "BLEED", meaning, the guitar will "BLEED" into the vocal mic and vice-versa. So, when you add an effect to one, you will inadvertently effect the other as well. If you want to have the flexibility to touch up your vocals with Auto-Tune or add a Lexicon Reverb to the guitar in post, then studio "Multi-Track" overdubbing is your only option. With studio overdubs, each instrument is recorded separately with no risk of “BLEED”. We simply record your guitar, in total isolation, to one track and later record an overdub of your vocals to their own independent track - all while monitoring the guitar performance through a pair of headphones. Now each can have their own independent effects treatment without one effecting the other.
Once these two sources have been captured to their own individual tracks, we could simply render them to a CD and your finished. However, if you would like your performance to sound flawless, with a final mix comparable to anything on the radio, and rendered to a format specific to your needs (e.g. CD, MP3, WAV files), then it will be necessary to Edit, Mix, and Master your recording.
Post Production and the Editing Stage
A) Noise Removal. We humans make a lot of little noises that we aren't immediately aware of during a recording session (e.g. sniffling, shuffling, swallowing, lip smacking, etc.). Then there's the occasional rustling of sheet music and room noises too. These noises are removed during the first phase of the editing stage.
B) Pitch Correction. Your vocals may require pitch correction to account for any stray notes. Tuning can be done automatically (e.g. Auto-Tune) or manually, via automation, it all depends on the voice in question. Tuning your vocals can definitely bring the production value of your song up a notch.
C) Comping. If your working to a strict tempo then "Comping" is something you'll want to seriously consider. Comping, is the method of splicing together multiple takes (e.g. takes with the best attributes) in-order to compile one perfect take. In the end you'll have a single flawless take that you can be proud of.
The Mixing Stage
Once the editing has been completed, the relative balance of guitar and vocal is adjusted during the mixing stage. Perhaps the vocal is not quite intelligible enough during the chorus but too prominent during the verse. Volume automation curves are created to bring the volume of individual tracks up and down as needed - automatically. Panning is used to give each instrument is it's own space in the mix. At this point, reverb or any special effects can be added to create space and dimension. Compression and equalization is used to add warmth, consistency and definition. These things and more are all within the scope of mixing.
The Mastering Stage
The overall tone and volume is addressed. A mastering equalizer is used to bring out subtle detail and add sweetening to the mix. Compression and limiting is used to minimize the overall dynamics in order to optimize the overall volume and add impact. If multiple songs have been recorded, the relative volume and tone of each track must match from song to song in order to bring cohesion and uniformity to the entire CD compilation. Fading out the end of each song and the relative space between each track is set. Finally, selecting your choice of the final format, whether it be audio CD, MP3, WAV, AIFF etc. is all part of the mastering stage.