first you need a wiring kit with fuse, you take the "live" wire (thickest one) and place the fuse at one end of it and attach the fuse to the battery. once uve done that you will need to find a path to feed it from the engine bay to the rear or were ever your amp is.
MAKE SURE THE FUSE IS UNPLUGGED FROM THE WIRE!!!!!
then you need to find a path for the earth wire to attach to (exposed metal) then finally you need to find the feed from your head unit and connect the feed to the amp. in your wiring kit it is a single thin wire once you have done all that and the wires are placed correctly into your amp you should have power and beable to feed it off to your subs and speakers