I finally figured it out. Thanks to everyone who helped me.
Here's a complete write up:
How to connect 12 Volt Power Outlet to Fuse Box
1. Ground the Black wire to metal part of the car. for example:
2. Look at your car's manual to see which fuse is not being used by your car. In the case of my Toyota Camry 2002, it was a 20A Seat Heater fuse.
Be sure to select a fuse which controls a part that is not permanently ON if you want the power to only be ON after you set the ignition power ON.
3. Get a Fuse Power Tap
from your Auto Parts store, for example Part # 85606 from here:
Connect the Red 12V line from your adaptor to it and insert one end of your fuse in between here:
so that when you put the fuse back in, it looks like this: