i have two 10 inch pioneer subs powered by a 1200 w rockford fosgate amp and i am getting a amp to power my back 6 by 9's 80 watt nominal each and i was thinking about installing a capacitor with my subs. 1. what is a capacitor 2. what does it do 3. where does it go. 4. what kind should i buy

if anyone could answer these i would greatly appreciate it thanks