You can download a full manual for the 12 here, which should assisst your son in the meantime.
There's a couple of ways to do the mixdown. Once all the tracks are as wanted, if there are 10 or less, you can do the mixdown straight onto say, tracks 11 and 12 and then once it's to his satisfaction, just connect the DPS outs to the ins of a CD burner and let it record in real time. Alternatively, you could just connect your outs to the ins of a CD recorder {or I presume, an interface of some sort} and mix straight to the CD. That would be my prefered method. I've been doing it that way with my old analog Tascam and I've grown used to it.
Hope that helps.
Take care, buddy,
Tagbo.