answer them in order if you can thanks..

1. there is rust in my trunk, on top of both wheel wells and on the side of another, what is the best thing i can do to stop it from further damage?
pictures:




2.What is the little button at the bottom of the dash?


3.What is this black box under the dash?


4.Whats this?


5.Whats this?


6.Whats the red light for?


7.Where is a good place to buy a better wire harness for a HID kit?


Sorry for all the questions im just trying to learn about all of this stuff its kinda newer to me
Thanks