this is easier to explain verbally but:
if this is your gear list ( plus your gits footpedals and processors etc )
1 mic
1 di box
cd player
synth
then on your mixer you would assign
ch1 to mic
ch2 to di box
ch3/4 cd player ( 3=L 4=R )
ch5/6 synth if stereo ( 5=L 6=R )
ch 7/8 could be for the computer playback ( say cubase ).....stereo again
the mixer should have at least 1 subgroub ( as opposed to the main o/p's )
the subgroup goes straight to the computer i/p ( record )
so if you want to record your git via an amp and mic....set the levels on ch 1 ..route the
signal to the subgroup ...it will automatically go to the DAW waiting to be recorded
any channel routed to the subgroup will be available for recording
when you play the computer back it will go through ch 7/8 ..through the main o/p's to
your monitors
any recording/playback senario can be achieved via the mixer
the whole point is....you can have an infinite amount of instruments
and sound modules at your disposal ( depending on your mixer ).....and once you've set it up thats it..no more plugging unplugging
etc
a good starting point for a mixer
is a 12.4.2 ie 12 inputs.. 4 subgroups ...stereo o/p