Nethunter - a few general questions

Hello everyone,

a few general questions to Kali Nethunter which I couldn't answer myself any other way and for my general understanding:

To begin with - what is Nethunter from a software point of view?
I did some research and implied by various installation-tutorials - eg. here - Nethunter itself is not another custom Android-ROM but a bunch of tools and scripts to build on top of an already operational Android. Did I get this right?
If yes, how in general does Nethunter alter my existing Android Setup, and what is shipped with Nethunter besides the Kali tools? A different kernel? Alternate drivers for hardware, etc?
How do I adress Nethunter once installed? Do I have to chroot into it (like LinuxDeploy for example) for everything I want to do with it or does it more like snap into my setup?

I'm thankful for every hint!

custom kernel that supports packet injection and usb attacks. you have chroot and a Nethunter app, Nethunter terminal and a few other apps.