To explain the DC-DC adapter:
If you wanted to use the standard plug, you would need an inverer. That turns 12v into 120v. then you plug your lapto into that. that big block on the laptop cord turns 120v into 12v. So oyu go 12v->120v->12v. The 12v adapter is just "12v". It wil lregulate the power to give you a "smooth" power. Basiacally filters out the bumps.
Things you're going to want/need:
Audio connection (hook it up to your stereo)