Okay,...
Say, for instance, you have a mixer or a Porta-format clone, and the principals are the same.
Your Inputs, [1-4] or [1-8] are routed through an "Assign" or "Group-Assign" section, which would typically be "L/R" or "1-2-3-4", depending on if you're on a simple Porta- or a larger one, or mixer.
In general, "L/R" applies to Track 1: Left, Track 2: Right, Track 3: Left, Track 4: Right", as well as being "Group 1:L", "Group 2:R", "Group 3:L", "Group 4:R".
Each "Track" or "Group"-assign has a button or switch, and then you'd rotate the PAN knob to differentiate your inputs between L & R.
Sorry if this explanantion is not the clearest synopsis.
For your Input 1, you may start by assigning it to Track or Group 1 & 2. Then, if you rotate Pan to the Left, Input 1 assigns exclusively to Track/Group 1, and rotate Pan to the Right, it assigns to Track/Group 2. Set PAN in the center, and you have equal amounts of signal routing to R/L, 1 & 2, equally.
Tracks or Groups 3 & 4 basically parallel the signal path on 1 & 2, with 3:L and 4:R.
Any input may be assigned to any output, (group) buss or track, through use of a combination of the Assign (group/track) switches (or buttons) and PAN.
Hope that's clear enough to get you started on the right track. I could only be more specific about the button names if I knew exactly which mixer you're talking about, but the principals are the same for every multi-buss mixer, and Porta-'s alike.
