This is the hello world package in Guix

(use-modules (guix packages)
             (guix download)
             (guix build-system gnu)
             (guix licenses))

(define-public hello
  (package
    (name "hello")
    (version "2.12.2")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnu/hello/hello-" version
                                  ".tar.gz"))
              (sha256
               (base32
                "1aqq1379syjckf0wdn9vs6wfbapnj9zfikhiykf29k4jq9nrk6js"))))
    (build-system gnu-build-system)
    (synopsis "Example GNU package")
    (description
     "GNU Hello prints the message \"Hello, world!\" and then exits.  It
serves as an example of standard GNU coding practices.  As such, it supports
command-line arguments, multiple languages, and so on.")
    (home-page "https://www.gnu.org/software/hello/")
    (license gpl3+)))

This is the hello world package in Nix

{
  callPackage,
  lib,
  stdenv,
  fetchurl,
  nixos,
  testers,
  versionCheckHook,
  hello,
}:

stdenv.mkDerivation (finalAttrs: {
  pname = "hello";
  version = "2.12.2";

  src = fetchurl {
    url = "mirror://gnu/hello/hello-$%7BfinalAttrs.version%7D.tar.gz";
    hash = "sha256-WpqZbcKSzCTc9BHO6H6S9qrluNE72caBm0x6nc4IGKs=";
  };

  # The GNU Hello `configure` script detects how to link libiconv but fails to actually make use of that.
  # Unfortunately, this cannot be a patch to `Makefile.am` because `autoreconfHook` causes a gettext
  # infrastructure mismatch error when trying to build `hello`.
  env = lib.optionalAttrs stdenv.hostPlatform.isDarwin {
    NIX_LDFLAGS = "-liconv";
  };

  doCheck = true;

  doInstallCheck = true;
  nativeInstallCheckInputs = [
    versionCheckHook
  ];

  # Give hello some install checks for testing purpose.
  postInstallCheck = ''
    stat "''${!outputBin}/bin/${finalAttrs.meta.mainProgram}"
  '';

  passthru.tests = {
    version = testers.testVersion { package = hello; };
  };

  passthru.tests.run = callPackage ./test.nix { hello = finalAttrs.finalPackage; };

  meta = {
    description = "Program that produces a familiar, friendly greeting";
    longDescription = ''
      GNU Hello is a program that prints "Hello, world!" when you run it.
      It is fully customizable.
    '';
    homepage = "https://www.gnu.org/software/hello/manual/";
    changelog = "https://git.savannah.gnu.org/cgit/hello.git/plain/NEWS?h=v%24%7BfinalAttrs.version%7D";
    license = lib.licenses.gpl3Plus;
    maintainers = with lib.maintainers; [ stv0g ];
    mainProgram = "hello";
    platforms = lib.platforms.all;
    identifiers.cpeParts.vendor = "gnu";
  };
})

A lot of the same skills and concepts transfer over, so if you're comfortable with Nix you don't have to lose all your skills and start over. I personally find the Guix package definition a lot more understandable than the Nix one.