Why do we need a C compiler?

[iampi31415]

Blogpost says

avr-gcc is a compiler that can take C code and create a binary source that can be uploaded to an AVR microcontroller.

Which C code are they talking about?
Could you describe the compilation process? (since it follows basically the steps in the readme on this project.)

I think it just runs rustc nightly but maybe is used afterwards to link our crate to some C dependencies, maybe the avr-libc? Why not use just ldd or some other linker?

I read instructions here.

[iampi31415]

I'm learning Rust, and have not coded in C ever, so that part is hard for me.

Does this project use https://github.com/rust-embedded/embedded-hal under the hood?