Vietnam War Question?

I’ve been doing some reading up on the Vietnam War and I’m a little confused about something.

Basically, my understanding of the war is that you’ve got Vietnam split up; the communist NVA with Ho Chi Minh to the north and the ‘democratic’ South Vietnam in the south.

So the North had the North Vietnamese Army (NVA) and the South had the allied forces (the US, Korea, etc) which were trying to aid the south Vietnamese army.

HOWEVER, the south also had the VietCong (VC) which were south Vietnamese guerrillas who were sympathetic to the North.

So here’s my question:
Was the majority of fighting (once the US had gotten completely involved in the war, after the Gulf of Tonkin Resolution) between the US and the VietCong (thus taking place in the south) or between the US and the NVA?

And where did the fighting with the NVA take place? Did the US go north into NVA territory and fight them or did the NVA mostly come south (such as with the Tet Offensive)?

I don’t really understand the geographic battle breakdown of the war. Because in movies and popular culture people only talk about the VC and “Charlie.” No one really mentions the NVA. So where did the fighting with the NVA take place and was that the majority of the war?