Commander is (meant to be) a toy operating system written from scratch.
Run nix-shell --run run-commander-vm. This will build and start a very light Commander OS VM for development purposes.
To build the EFI FAT image, run nix-build -A distro.bootImage in the root of the repo. You'll find the built image in result/boot.img.
To build the kernel, run nix-build -A pkgs.kernel. You'll find the built kernel in result/bin/kernel. To run it, use the Limine bootloader.