Let's simplify this even further. As @H2Only stated:
Ext. In 1 = Left Audio Channel
Ext. In 2 = Right Audio Channel
Ext. In 1+2 = Stereo Pair of Audio Channels. Left (1) + Right (2).
Computers
Most people start learning about recording with laptops, so let's use that for this example. A laptop usually has 2 audio ports that are for 1/8" (3.5 mm) mini plugs. One of the ports is for audio output (headphones, speakers, etc.), and the other one is for audio input (microphone, CD player, etc.), and
both of those audio ports are stereo pairs.
But wait! A single microphone is mono. How does that work with a laptop's input port that is a stereo pair? Well, that depends on the cable used to connect the microphone, and most (if not all) cables will present the audio from a microphone to both the Left and Right audio channels.
Ableton Live
Therefore, your voice ends up being presented to both the Left (1) and Right (2) audio channels in Live, and you end up recording the same thing regardless of which input (Ext. In) you choose. Make sense?
So given that, are there any ways to get the microphone presented to either the Left or Right audio channels, and not both? Maybe.
Some sound cards have little application consoles that allow you to mute one of the stereo audio inputs (left/right pair), which would allow Live to record one of the two, but not both at the same time. Not a very good option.
However, you could purchase an audio adapter/cable at an electronics store that has a stereo mini plug on one end and 2 mono (1 Left & 1 Right) mini plugs on the other end, but...
TBonezzz wrote:Well, what I'm wondering, is can I record my mic and stereo mix at the same time, but on their own separate tracks?
Based on the information you've given us, the answer is no.
Why? Because your sound card only has a left/right pair for audio inputs, which can only be used to record the Left (1), the Right (2), or Left/Right (1+2) together. To record a mono microphone, and a stereo pair (left/right) at the same time on separate tracks requires more than a left/right pair of audio inputs.