its fairly easy, make sure you use a good wiring kit, they do sell multi amp kits as well, basically its one heavy wire from the + on the battery, to a distubution block, power wire to each amp, ground everything, also a good idea to get a capacitator, (included in some kits). Power wire should be run under the trim on one side of the car, usually passenger side, and then a rca patch cable and remote wire from the headunit to the amps, some headunits have more than one output, one for the subs and one for the speakers.
Depending on the power of th system, you may need to upgrade the alternator and battery in your car