noob, head unit, 2004 taurus

First HU installation so bear with me. I have a 2004 Ford Taurus SE. My factory amp is in the trunk here, as you can see. I got the mounting kit, and the HU into place. This is the wiring harness that came with the mounting kit. Now what I thought would happen is the wiring harness goes from the new head unit (spliced together) and the wiring harness would plug directly into the amp. But again, I’m a noob, so maybe that is a stupid assumption. What I did notice was that the first wire that plugs into the outlet in the amp fits into the wiring harness. So now I’m really confused. Where do I plug the wiring harness?