i have just bought ben's book and it is phenomenal. although i am confused with the part where i put a phonojack in? i thought a phonojack for for audio...why do i have my DC auxillary jack getting connected to it? probably a dumb question but hopefully someone can help me understand.

It's probably just being used for power.

The thing is just a jack, a plug, it has no "set purpose", you could use it for just about anything that uses two wires.

So, in this case, it's being used for power, apparently.

It's because Ben was kinda rushed to write the book, so he probably just said "okay this jack'll work" and used it. Don't worry about it, it's correct, just odd.