Sub and Amp Installation Help

I have a 2001 oldsmobile alero gls. Sick of the stock sound so i'm adding 2 12s, an amp, and an aftermarket deck. I know the oldsmobile alero has a stock monsoon sound system with an amp already. So i just wanted to make sure i was installing these the right way. So do i just need to put in the deck connect it with the wiring harness... then wire the amp to the battery and connect it to the aftermarket deck? Will my sound work? Not really sure what to do... any help would be appreciated!

you need the os 2 integration wiring harness $100 plus shipping for it ,then you need an amp kit